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Visualizing the Fort

AN INVESTIGATION INTO THE USE OF 3D MODELLING FOR THE CONSERVATION

AND RESTORATION OF A FORT OF THE DEFENCE LINE OF AMSTERDAM

Emma Egberts 11956771

MA Conservation and Restoration of Cultural Heritage, University of Amsterdam

Specialization: Historic Interiors

Supervisor: M. N. (Merel) van Schrojenstein Lantman, MA Date: 21-08-2020

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Summary

In this thesis, the use of 3D modelling technology for the conservation and restoration of cultural heritage has been investigated. This has been done specifically by studying the advantages and disadvantages of the use of the modelling program Blender for the case study of Fort benoorden Spaarndam. This is a military fort dating from the beginning of the 20th century and is part of the Defence Line of Amsterdam. In this fort, multiple wall paintings and decorative painting schemes have been found under layers of white overpaint. The decorations in room 23 have been investigated through architectural paint research, showing that five different decorative paint schemes have been present over time. These paintings are being threatened by two factors: the bad climate conditions in the fort, resulting in deterioration of the paint layers and the, still unknown, plans for the future function of the fort. It has been found that 3D modelling technology can create useful opportunities to deal with these problems, by documenting the current state of the fort, visualizing and

reconstructing the historic phases and by disseminating these to a public in an immersive or interactive way. For the use of 3d modelling for conservation and restoration of historic interiors, Blender has advantages and disadvantages compared to other 3D modelling techniques. The disadvantages are that it is not directly based on recordings of reality, resulting in a less accurate model, or a model that can not be seen as an exact documentation of reality. The use of laser scanners or structured light scanners are a better option for this, for example to study the surface of a painting in high detail or to survey the condition of a building over time. These techniques are still relatively expensive and require the need of a skilled professional. Photogrammetry is, compared to laser scanning, a more affordable alternative, making use of photography, but does not record surface texture. The advantages of Blender however are its relatively easy use and the fact that it is available on the internet for free, making it a great option for projects with limited financial options and people with little experience in digital modelling. Next to this, it gives the modeler complete control, which is useful for creating a model that shows exactly what you want to show, making additions or reconstructing things that do not exist anymore.

Abstract

In this thesis, the use of 3D modelling technology for the conservation and restoration of historic interiors has been investigated. This has been done specifically by studying the advantages and disadvantages of the use of the modelling program Blender for the case study of Fort benoorden Spaarndam, compared to other modelling technologies.

Abstract (Dutch)

In deze scriptie is het gebruik van 3D-technologie voor conservering en restauratie van historische binnenruimten onderzocht. Hierbij is specifiek gekeken naar de voor- en nadelen van het modeleer programma Blender voor de case study van Fort benoorden Spaarndam in vergelijking met andere 3D-modelleer technieken.

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Inhoud

Summary ... 1 Abstract ... 1 Abstract (Dutch) ... 1 Introduction ... 4

Chapter 1: Fort benoorden Spaarndam ... 5

1.1 Metadata ... 5

1.2 Fort benoorden Spaarndam ... 5

1.3 Defence Line of Amsterdam ... 8

1.4 Decorations ... 10

1.5 Condition, conservation and restoration issues ... 13

1.6 Other forts with wall paintings ... 16

Chapter 2: Future fort ... 23

2.1 New functions for forts within the Defence Line ... 23

2.2 Involved parties ... 23

2.3 Preservation of the wall paintings ... 24

Chapter 3: Architectural paint research in room 23 ... 26

3.1 Introduction room 23 ... 26

3.2 Research techniques ... 28

3.3 Results of sample analysis ... 29

3.4 Results of stratigraphies ... 33

3.5 Dating of the layers ... 36

Chapter 4: 3D modelling technology ... 40

4.1 Laser-scanning ... 40

4.2 Structured Light Scanning... 41

4.3 Photogrammetry ... 42

4.4 3D modelling programs ... 43

Chapter 5: Modelling process in Blender ... 44

... 47

Chapter 6: Possibilities 3D models ... 47

6.1 Documentation ... 48

Visualization ... 55

Dissemination ... 59

Chapter 7: Limitations ... 62

7.1 Limitations of 3D models ... 62

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3 Conclusions ... 65 Acknowledgements ... 66 Bibliography ... 67 Appendix 1. Room 23

Appendix 2. Overview decorations room 23 Appendix 3. Overview Stratigraphies Appendix 4. Samples locations Appendix 5. Sample Analysis

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Introduction

3D modelling technology has been used within the field of cultural heritage for multiple decades and is becoming more and more popular. However, professionals working the area of conservation and restoration of historic interiors have been more hesitant to use this technology, possibly because it is often thought to be expensive, difficult or not adding enough value. However, different techniques to create 3D models are available, with their own price range, use and results. One cheap and accessible way is the use of Blender, a free online-accessible modelling program in which a 3D model can be created without the need for expensive equipment.

In this thesis, the use of 3D technology for the field of historic interiors will be investigated. This is done by discussing the advantages and disadvantages of different modeling

technology and comparing the use of Blender to these. A case study will be used to test the usefulness of Blender for the field of historic interiors. The case study that is being used is Fort benoorden Spaarndam (also called Fort Benoorden throughout this thesis). This is a military fort dating from the beginning of the 20th century that is part of the UNESCO protected world heritage Defence Line of Amsterdam. Within this fort, many wall paintings and painted decorative schemes have been found under layers of white overpaint. However, the preservation of these wall paintings is being threatened by two factors: the bad climate conditions in the fort and possible changes to the function of the fort. In this thesis it will be discussed how 3D models can be a great addition when dealing with these problems, by documenting and ‘preserving’ the paintings in in a digital way.

First, Fort benoorden Spaarndam and the conservational issues will be introduced. Then, the architectural paint research carried out will be discussed. After this, the different available 3D technologies will be explained, after which the creation of a 3D model of Fort Benoorden in Blender will be discussed. The use of Blender will be discussed by focusing on three areas that are important for the conservation and restoration of historic interiors: documentation, visualization and dissemination. The advantages and disadvantages of Blender for these areas will be compared to the other available 3D technologies, namely photogrammetry, laser scanning and structured light scanning. Through examples of other projects in which 3D models have been used, the possibilities for Fort benoorden Spaarndam will be

highlighted. After this, the limitations of 3D models in general will be discussed shortly. Finally, some final thoughts and recommendations for future research will be discussed.

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Chapter 1: Fort benoorden Spaarndam

1.1 Metadata

Name: Fort benoorden Spaarndam

Address: Visserseinde, 2063 JD Spaarndam

Part of: Stelling van Amsterdam (Defence Line of Amsterdam) Protected provincial monument Noord-Holland

1.2 Fort benoorden Spaarndam

Fort benoorden Spaarndam is a fort located in the Westbroekerpolder in Spaarndam, near Haarlem and forms the Position of Spaarndam together with Fort bezuiden Spaarndam. It has been built around 1885 and 1901 and could hold up to 299 soldiers and around 20 higher ranked officers. More men could be housed in the smaller buildings surrounding the fort, the ‘bergloods’ (destroyed by fire in 1924) and the ‘troepenloods’.1

The forts were designed to be small and low, to fit within the landscape, making it harder to target them. Earlier forts were built with bricks, but for the Defence Line of Amsterdam the then new material concrete was used.

The fort building is classified as a Type A, a type of fort used between 1897-1907.2 This type consists of two buildings, a front building and a main building which are connected through a long hallway (called the Poterne). The front building usually has seven rooms for the guarding unit and a storage for munition, while the main building was used as the living spaces and storage rooms. Located here were the rooms for the soldiers with bunk beds, the more luxurious rooms for the higher officers and the common rooms such as the kitchen and hospital. These rooms are all similarly shaped: a rectangle with a vaulted ceiling and four doors leading to the next rooms. The east wall contains a door to the outside and two deep window-niches. The longer north and south walls also have wooden beams that have been built in the wall, which have been used to connect shelving to the wall or create a division in the room.

1 “Fort benoorden Spaarndam”, Stelling-Amsterdam, accessed 01-07-2020,

http://www.stelling-amsterdam.nl/forten/spaarndam-noord/

2 Fort types, Stelling-Amsterdam, accessed 03-07-2020,

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6 Figure 1 Fort benoorden Spaarndam, back side. Photo: author.

Figure 2 Fort Type A, Source:

https://www.stellingvanamsterdam.nl/nl/historie/stelling-van-amsterdam

\

Figure 3 Fort benoorden Spaarndam. Source: RCE

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7 Figure 4 Layout Fort benoorden Spaarndam. Source: Z. Ziegelaar

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1.3 Defence Line of Amsterdam

Fort benoorden Spaarndam is part of the big network of military buildings that form the Defence Line of Amsterdam. This system was built between 1880 and 1918, as a way of defending Amsterdam based on an inundation mechanism, creating the possibility of flooding an area of land between 3 and 5 kilometers wide. The Defence Line is comprised of thirty-six forts, two coastal forts, two fortresses, four batteries and two coastal batteries.3 The Defense Line of Amsterdam was not the first defense mechanism based on inundation in the

Netherlands, the Position of Den Helder (started around 1574), the Dutch Waterline (started 1672) and the New Dutch Waterline (from 1815 on) are earlier examples. Because of

increasing threat from neighboring countries during the French-Prussian war of 1870-1871, a Defense Line around Amsterdam was created. This version was still very basic and minimal. On April 8th of 1874, the Fortress Law was passed, giving way to the development and modernization of the Defense Line.4

3 “Introduction”, Stelling-Amsterdam, accessed 01-07-2020,

http://www.stelling-amsterdam.nl/english/common/introduction/index.php.

4 “Defenisve Lines”, Stelling-Amsterdam, accessed 21-08-2020, http://www.stelling-amsterdam.nl/english/lines/netherlands/index.php.

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9 Most of the forts were unoccupied during peacetime, except for the two coastal forts of IJmuiden and Pampus. When the First World War started, only some parts of the Defence Line had been completed but in 1920 the build was finished. In many cases, additions were made to the forts during the First World War. The mobilization for the First World War started on the 31st of July, 1914 and by the 2nd of August all forces were stationed at the forts. In total around ten thousand soldiers were based in the forts. Most of the forts stayed occupied until the end of the war in 1918.5During the Interbellum, some forts were used as a prison for

punished soldiers or conscientious objectors. At the start of the Second World War, however, many forts quickly became occupied by the Germans. The German army invaded the

Netherlands on 10 May 1940 and the Dutch capitulation was already declared before the Germans had reached the Defence Line. The German occupiers also made additions and changes to the forts. After the war ended, some of the forts were once again used as

prisons, such as Fort Spijkerboor.6 From the 1950s on most of the forts were used as a place to store munition or as a workplace to dismantle old munition. The advantages of the system of inundation and the need for a permanent defence mechanism diminished after the war and the forts officially lost their status as defence mechanism between 1956 and 1960. 7

As mentioned above, Fort benoorden Spaarndam was first in use during World War I. It is known that the third battalion of the Second Regiment ‘Vesting’-artillery (2.R.V.) was based in the fort during the First World War and shortly after and also parts of the 7th Regiment Infantery are thought to have been stationed at the fort during the first World War.8 More is known about the occupation of the fort during the Second World War. Dutch soldiers were stationed here at the beginning of the Second World War. Some signatures are left on a door, dated 17 May 1940, when a few Dutch soldiers were still stationed at the fort after the capitulation of 14 May while waiting for further instructions.9 Sometime after that, the fort became occupied by German troops.10 Sources mostly mention occupation by German troops in 1944, but because of the early date of the capitulation it can be expected that the

5 “Tijdlijn 1914-1945”, Stelling-Amsterdam, accessed 01-07-2020,

https://www.stellingvanamsterdam.nl/nl/historie/tijdlijn-van-de-stelling-van-amsterdam/1914-1945.

6 “Fort Spijkerboor”, Stelling-Amsterdam, accessed 01-07-2020,

http://www.stelling-amsterdam.nl/forten/spijkerboor/

7 “Tijdlijn 1945-1960”, Stelling-Amsterdam, accessed 01-07-2020,

https://www.stellingvanamsterdam.nl/nl/historie/tijdlijn-van-de-stelling-van-amsterdam/1945-1960

8 ”Fort benoorden Spaarndam”, Stelling-Amsterdam, accessed 01-07-2020,

http://www.stelling-amsterdam.nl/forten/spaarndam-noord/

9 J.A.T. Wijnen and Nico van der Woude, Muurschilderingen en Decoraties in Fort benoorden

Spaarndam. Nulmeting, waardering, plan voor behoud (Wageningen: Wijnen Cultuurhistorisch Onderzoek, 2015), 36.

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10 fort was occupied by the German troops earlier than 1944. The first known mention of

German groups is by resistance group Groep Albrecht, that mentions the presence of around 300 men on June 12, 1944, with a sign saying ‘Wassowsky’. This can be interpreted as a reference to the Fallschirm Ersatz- und Ausbildungs-Regiment Hermann Göring (part of Batallion Wossowsky) , which was a group of young soldiers training for the Luftwaffe. A day later, the resistance group mentions men from Luftwaffe troops, possibly from this group.11 These men left before July 2nd 1944 and were replaced by 100 (and later up to 300) SS-soldiers. On August 3rd, Group Albrecht mentions 200-250 men of the 6th compagnie SS (Polizei Division). All German troops are thought to have left around August 25, 1944.12 From the 1950s on, the Defence Line was being dismantled and Fort Benoorden lost its function as a defence building in 1951. After that, it was used as a storage space for munition of the navy, but from the 1970s on it was mostly empty.13

1.4 Decorations

In the fort, many wall paintings and painted decorations have been discovered under layers of white overpaint. Different researchers were brought in to investigate the fort’s history and the condition of these wall paintings. In 2007, research was done by Beek & Kooiman Cultuurhistorie together with Bureau M&DM. This research focused on documenting the fort and the paintings that had been discovered so far.14 In 2009 Stichting Krayenhoff

commissioned three conservators to look into the condition of the paintings and necessary

11 “Fallschirm Ersatz- und Ausbildungs-Regiment Hermann Göring”, Katwijk in Oorlog, accessed

01-07-2020, http://katwijkinoorlog.nl/fallschirm-ersatz-und-ausbildungs-regiment-hermann-goring/ 12Wijnen, Muurschilderingen en Decoraties, 12.

13 Wijnen, Muurschilderingen en Decoraties, 10.

14 Mattie, Erik and Marijke Beek. Cultuurhistorisch Vooronderzoek. Fort Benoorden

Spaarndam, (Amsterdam: Beek & Kooiman Cultuurhistorie, M&DM), 2007.

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11 conservation treatment.15 More recently, research into the condition of the paintings and the conservational needs of the fort is continued by Jobbe Wijnen and Nico van der Woude. 16 Their research focuses on the history of the building in general and the different decorations that have been found, creating an indexation of the decorations present and a value

assessment of the different decorations and rooms.17 However it is likely that there is still a lot that has not been discovered yet or that has been lost (either in the past or during the uncovering). This categorization consists of 7 categories:18

1. Functional paintwork: room names and numbers 2. Decorative paintwork: wainscoting, stenciled borders

3. Figurative paintings and drawings: artistic expression, made by hand. Different themes: military, rural/farmer, women, cartoons

4. Slogans

5. German slogans, drawings and paintings: different decorations linked to the German occupation

6. Signatures

7. Miscellaneous/modern graffiti

Some rooms contain a lot of the different decorations, while some contain only one or two. The decorative stencil work can be found in most of the rooms but are mostly all different in pattern and colors. The slogans can be found in three different rooms, carried out in a big size on the walls, in a colored and placed in a decorative framework. In three of the rooms drawings and slogans have been found that can be linked to the German occupation of the fort. These contain SS-signs, but also drawings with German texts and signatures. Other decorations could also be from the time of the German occupation but cannot be connected to this phase for certain.

Signatures of people have been found in different locations in the fort. Some of them have been dated, showing the signatures are from different phases of the use of the fort. Most of the signatures date from people from the navy who were in the fort in the 1950s, however also signatures from 1940 have been found. Finally, a lot of modern graffiti is visible

throughout the fort. These have been made with modern materials and are of low artistic and

15 Crèvecoeur, R., P. Dijkman, P & C. Junge. Behoud schilderingen in fort benoorden Spaarndam

(brief aan de Stichting Krayenhoff), 2009.

16 J.A.T. Wijnen and Nico van der Woude. Muurschilderingen en Decoraties in Fort benoorden

Spaarndam. Nulmeting, waardering, plan voor behoud. (Wageningen: Wijnen Cultuurhistorisch Onderzoek, 2015).

17 J.A.T. Wijnen and Nico van der Woude. Muurschilderingen en Decoraties in Fort benoorden

Spaarndam. Nulmeting, waardering, plan voor behoud. (Wageningen: Wijnen Cultuurhistorisch Onderzoek, 2015).

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12 historical value but give an insight into the loss of function of the fort and its slow decay over the last decades of the twentieth century.

Figure 7 painting in the Poterne. Photo: author.

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13 Figure 9 stenciled decoration. Photo: author

1.5 Condition, conservation and restoration issues

Research into the condition of the fort has been carried out by Nico van der Woude in 2015.19 The condition of the building in general is relatively bad. Due to loss of function, the building has been neglected and not maintained, resulting in degradation of the building. People entering the building illegally has resulted in graffiti on many walls throughout the fort (see fig. 10). However, the biggest influence on the degradation has been due to climate, mostly because of moisture. The temperature and the relative humidity have been measured in different rooms over a few months. This has shown the relative humidity to be very high, fluctuating between 67,1% and 91,5%.20 This has resulted in the biggest moisture problems in the spring, when the temperature within the building is still low but the warm outside air contains a lot of water. When this air enters the building, for examples when doors or windows are opened, this creates condensation on the cold walls inside the fort, resulting in water damage to the walls and the paintings. Next to that, damages to the roof and clogging of the iron water-drains in the walls has resulted in rainwater entering the building, causing

19 N. van der Woude, Fort benoorden Spaarndam. Onderzoek naar conditie en conservaring van de

schilderingen. (Stichting Restauratie Atelier Limburg), 2015.

20 N. van der Woude, Fort benoorden Spaarndam. Onderzoek naar conditie en conservaring van de

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14 more water damage throughout the fort. In the winter, the water has frozen and caused cracking in the walls. Dripping of water is visible on the walls, where it has resulted in discoloration and transfer of dirt and salts (fig. 11-14). The moisture in the walls also results in the efflorescence of salts. In the wooden elements of the fort, the moisture has led to the formation of fungi and overall degradation of the wood.

The moist conditions have also had a big effect on the wall paintings. The paint used on the walls is a chalk-based paint, which is hygroscopic and very susceptible to water. Because of this, the paint layers have become moist and powdery in many places, due to decreasing binding power of the binding medium. In other places the paint layers have become very rigid and dense, probably because of chemical changes from material used in the concrete walls. Next to this, the transfer of salts has and the cracks in the walls have resulted in delamination of the paint layers in many places, resulting in a disturbed surface and a disturbed experience of the decorative painting schemes (fig. 15). Additionally, there is a lot of discoloration visible on the most recent painting scheme, probably resulting from water damage and transfer of dirt. The leaks in the roof have been fixed, removing a big source of the water damage, but the shifts in relative humidity and condensation in the spring still form a damaging factor. Besides climatological damage, the fort was filled with moths and spiders. Most of these have been removed. The moths are likely to return if the conditions in the fort are not changed.

Finally, the wall paintings have been uncovered to some extent. However, it proved very difficult to completely uncover the paintings without loss of paint. Next to that, in most cases also a haze would stay visible on top of the uncovered painting because of it being difficult to completely remove the overpaint. Removing the layers of overpaint often results in quite a lot of damage to the paintings, impossible to remove the overpaint without damaging the paintings to some extent.

Currently visible in the room is a disturbed experience of the room, due to the degradation of the fort in general, dirt accumulation, discoloration and paint loss. However, also the visibility of multiple decorative paint schemes within the walls causes a disturbed image. The wall paintings are visible in combination with the most recent painting phase. This shows a wrong representation of the paintings. Instead they should be experienced within the coherent decorative framework in which they have historically been visible.

To ensure the conservation of the fort in general and the wall paintings more specifically, the indoor climate conditions should be stabilized to decrease damage to the paint layers. Next to this, the currently sensitive paintings should be consolidated, but more research into this is needed. Besides consolidating and stabilizing the climate, the future function of the fort is another important factor for the conservation of the paintings. A function for a historic building is often needed to create financial options for maintaining the building

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15 and creating interest and valuation for its safeguarding. This could result in a public function with a connection to the history of the building such as a museum, in a more private function when used by a company or business or in a combination of public and private functions. The use of 3D models can be a useful addition for most of the different scenarios for the future of the fort, as will be discussed inchapter 6.

Figure 10 Graffiti-artist 'Joel' in room 29.

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1.6 Other forts with wall paintings

The wall paintings at Fort benoorden Spaarndam are not a stand-alone example. The fort is unique in the fact that it contains many wall paintings that seem to date from different periods of use of the fort, but a few other forts of the Defence Line are also known to have wall paintings. However, documentation and research is not available for most of these forts, showing the need for a better documentational framework collecting research into multiple forts in one location. The use of decorations and artistic or individual expressions are thought to have been more common in forts and military buildings, ranging from organized projects to graffiti, even though little research has been done on this topic.21

21 Military graffiti has been described in:

Figure 14 Salt and surface dirt on paintings in room 15. Source: Jobbe

Wijnen Figure 13 Deterioration of the paintings. Room 23. Source: Author

Figure 16 Paint flaking off in room 23. Source: Author Figure 15 White haze and discoloration. Source: Jobbe Wijnen

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17 At Fort bij Nigtevecht, now used as meeting rooms and a café, two soldiers are said to have painted scenes from the life of the soldiers in the canteen between 1914 and 1918. 22 However, no evidence of these paintings could be found, except for it being mentioned in text.23 In Fort bij IJmuiden, opened to the public once a month, a few wall paintings dating from the German occupation during the Second World War have been found (see fig. 17 and 18).24 These wall paintings have suffered mostly from vandalism and paint loss.

Jobbe Wijnen, "'Vermaas, la vache qui rit'. Militaire graffiti als bron voor archeologisch en historisch onderzoek naar alledaagse militaire cultuur," Tijdschrift voor geschiedenis 131, no. 1 (2018): 143-154. Kenny Brouwers, “The Walls as a Silent Witness to it All: a Preliminary Introduction to Conflict Related Graffiti,” Kunsthistorisch Tijdschrift Desipientia 21, no. 2 (2014): 24-28.

22 “Fort bij Nigtevecht”, Stelling-Amsterdam, accessed 21-08-2020,

http://www.stelling-amsterdam.nl/forten/nigtevecht/index.php. No images were found.

23 “Soldaat Meijer”, Stelling-Amsterdam, accessed 21-08-2020,

http://www.stelling-amsterdam.nl/mensen/overig/eerste-wereldoorlog/index.php#MEIJER.

24 Timeline of the Defence Line of Amsterdam, 1914-1945, Stelling van Amsterdam,

accessed 21-08-2020. https://www.stellingvanamsterdam.nl/nl/historie/tijdlijn-van-de-stelling-van-amsterdam/1914-1945.

Figure 17 Paintings at Fort bij IJmuiden. Source: festungsbauten http://www.festungsbauten.de/NL/Amsterdam_Ijmuiden.htm

Figure 18 Paintings at Fort bij IJmuiden. Source: festingbauten. http://www.festungsbauten.de/NL/Amsterdam_Ijmuiden.htm

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18 Another fort containing wall paintings is the other fort of the Position of Spaarndam, Fort bezuiden Spaarndam. These paintings are copies of paintings from the Rijksmuseum, such as ‘Sinterklaasavond’ by Jan Steen (see fig. 19-21). Their artistic quality is higher than the paintings from Fort Benoorden, but they are in relatively bad condition.25 It is unknown from what time these paintings date. Another interesting example from this fort is the painting of a landscape above an embrasure. This landscape would have mirrored the landscape that is

visible through the opening, helping the soldiers aim in foggy weather. Historic images of the fort show that stenciled borders have been present here as well (fig. 22.) The walls had at some point been painted in yellow with a black painted plinth, but besides this very little is known about the decorative paintwork in this fort. Fort Bezuiden Spaarndam has been developed into a multifunctional location, with a café, small museum about the Defence Line and a small exhibition room. It also offers options for renting boats and organizing events.26

25 Mattie and Beek, Cultuurhistorisch Vooronderzoek, 19.

26 “Fort Zuid”, Forten.nl, accessed 21-08-2020, https://forten.nl/forten/fort-zuid/.

Figure 20 Wall paintings in Fort bezuiden Spaarndam. Source: Author

Figure 19 Close-up of painting at Fort bezuiden Spaarndam. Source: tripadvisor

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19 Figure 22 Copy of photo showing stenciled decorations in Fort bezuiden Spaarndam. Source: author.

Another fort from the Defence Line that contains figurative paintwork is Fort bij Spijkerboor. During the Second World War it was used as a detention center for soldiers and after the war for war related criminals.27 The wall paintings in the Poterne are thought to have been made by one of the prisoners around 1945-1946.28 They are visible together with a yellow-blue wall. Next to that, there is also a small decorated chapel in the fort (fig. 23 and 24).29 The fort has been restored and the paintings are presented in a museum-like setting, with a

protective covering and spotlights. This fort is also open for visitors on a limited basis.

27 “Fort bij Spijkerboor”, Stelling van Amsterdam, accessed 21-08-2020, https:

//www.stellingvanamsterdam.nl/nl/fort-bij-spijkerboor.

28 “Fort bij Spijkerboor”, Stelling-Amsterdam, accessed 21-08-2020,

http://www.stelling-amsterdam.nl/forten/spijkerboor/index.php.

29 “Fort bij Spijkerboor”, Oneindig Noordholland, accessed 21-08-2020,

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20 Figure 23 Paintings at Fort Spijkerboor. Source: rondomkijken.nl

Figure 24 Paintings in the Poterne at Fort Spijkerboor. Source: rondomkijken.nl

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21 Next to the figurative paintings found in these forts, a similar example of stencil decorations has been discovered in Fort aan den Ham. No research into this discovery has been published, but pictures posted on the website of the fort show an uncovered part of the wall with traces of the stenciling decorations in two rooms, of the higher ranked officers and fort commander, which has been replicated on the other walls of these rooms (fig. 26 and 27).30 This fort has been restored to some extend as well, with a reconstruction of the rooms of the higher ranked officials and the hospital room. Other parts of the fort are in use as exhibition rooms for a military museum.31 Stencil decorations are also said to have been found in the room for the officers at Fort bij Krommeniedijk, but these have not been documented and are currently not visible.32

30 Blogpost 2 January 2013, Fort aan den Ham, accessed 21-08-2020,

https://www.fortaandenham.nl/cms/blog/page/6/.

31 Fort aan den Ham, accessed 21-08-2020, https://www.fortaandenham.nl/cms/. 32 Fort bij Krommeniedijk, Stelling-Amsterdam, accessed 21-08-2020.

http://www.stelling-amsterdam.nl/forten/krommeniedijk/index.php.

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22 Figure 27 Screenshot from video of Fort aan den Ham. Room of the fort commander with stencilled decorations. Source: https://www.fortaandenham.nl/cms/fort-rondleiding/

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Chapter 2: Future fort

2.1 New functions for forts within the Defence Line

After the forts of the Defence Line lost their function from the1950s onwards, a small number has gotten a new function.33 Some have been given a museum function, offering tours, exhibitions and events related to the history of the fort or the Defence Line, such as Fort Pampus and Fort bij Krommeniedijk.34 Other forts are opened to the public on a more limited scale. Fort bij Edam has limited access for visitors, keeping the fort relatively unaltered since the 1980s.35 Next to forts keeping their link to the history of the Defence Line, some forts have been given a more commercial destination, such as locations for events, restaurants or exhibitions. For example, Fort aan de Nekkerweg has been changed into Fort Resort

Beemster, a spa resort.36 However, the majority of the forts of the Defence Line has not been opened to the public.

2.2 Involved parties

The complex of the buildings of the Position of Spaarndam has already been a provincial monument since 1990 and in 1996 the Defense Line of Amsterdam as a whole has been recognized as World Heritage by UNESCO. 37 However, in practice this mostly means protection of the structure of the Defence Line, not specifically protection for the interiors of the forts. On the website of UNESCO, plans are stated to create three visitor centers from the Defence Line, at Fort Pampus, Fort bij Krommeniedijk and Fort Benoorden Spaarndam.38 The first two have been developed into museums where focus has been placed on

33 The different new functions of forts of the Defence Line have been described in:

T. Lycklama, A.J.T Goorts, A.C. Riefel and E. van der Woude. De Stelling van Amsterdam bekent kleur. Van erfgoedlocatie naar toeristische trekpleister van wereldformaat, Bureau voor Ruimte & Vrije Tijd, 2016.

34 Fort bij Krommeniedijk, Stelling van Amsterdam, accessed 21-08-2020,

https://www.stellingvanamsterdam.nl/nl/forten/de-stelling-op-de-kaart/detailpagina-fort/q/id/144/title/fort-k-ijk-fort-bij-krommeniedijk.

Forteiland Pampus, Stelling van Amsterdam, accessed 21-08-2020.https://www.stellingvanamsterdam.nl/nl/forteiland-pampus.

35 Website of Fort bij Edam, accessed 21-08-2020. https://www.fortbijedam.nl 36 Fort aan den Nekkerweg, Stelling van Amsterdam, accessed 21-08-2020.

https://www.stellingvanamsterdam.nl/nl/fort-resort-beemster-fort-aan-de-nekkerweg Fort Resort Beemster, accessed 21-08-2020. https://www.fortresortbeemster.nl/

37 More than 125 elements of the Defence Line are provincial heritage monuments and around 25 are

state monuments. Website of Unesco World Heritage, accessed 21-08-2020. https://whc.unesco.org/en/list/759/

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24 experience and education, linking the forts to the history of the Defence Line.39 However, this has not been the case for Fort benoorden Spaarndam, for unknown reasons. After having been neglected for over thirty years since the 1970s, the buildings and the area surrounding Fort benoorden Spaarndam attracted the interest of different parties at the beginning of the twenty-first century. These parties are concerned about the future use of the fort and the surrounding area and about the preservation of its history and paintings. Officially, Fort benoorden Spaarndam is still owned by the Ministry of Defense, but Recreatieschap

Spaarnwoude is the functioning owner, meaning that they make decisions regarding the use of the fort. The Recreatieschap is a group managing the use and development of the general area of Spaarnwoude, such as the nature and recreation options.40 They are also managing the developing plans for the future of the fort and initiated research into its history and conservation needs. One of the big parties working together with the Recreatieschap is Stichting Krayenhoff, a foundation which was established in the 1990s to open the other fort in Spaarndam, Fort bezuiden Spaarndam, for a bigger public. After this project was finished, they shifted their attention to Fort benoorden Spaarndam in 2003 and started research into the fort and the possibilities for its future. Stichting Krayenhoff and their volunteers since have been involved in the uncovering of the paintings and cleaning of the fort.41 Another party involved in the future of the fort is BOEi, a company focused on restoration and creating a new destination for monuments.42 This company is currently conducting a

research into the interest and possibilities of involvement of the local communities, to create a support base for possible plans.43

2.3 Preservation of the wall paintings

Due to the bad condition of the fort and the wall paintings, the future of the fort is still

uncertain. The conservational issues are still being investigated at the time of writing and are being taken into account in the development of the plans for the fort. It is still unknown how and if the wall paintings will be incorporated within this new function. The large amount of paintings, combined with the historical context of the fort and the fact that this fort has been relatively unaltered since the 1950s, make it a unique and valuable example of military history, which gives an interesting look into the use of the fort in the first half of the twentieth

39 “Belevingsroutes”, Pampus, accessed 20-07-2020,

https://www.pampus.nl/op-pampus/belevingsroutes/

Fort Kijk, Forten.nl, accessed 20-07-2020, https://forten.nl/forten/fort-bij-krommeniedijk-fort-kijk/

40 “Visie”, Spaarnwoude.nl, accessed 20-08-2020, https://www.spaarnwoude.nl/visie. 41 Wijnen, Muurschilderingen en Decoraties, 15.

42 Website BOEi, accessed 19-08-2020. https://www.boei.nl/.

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25 century. This makes it desirable to save the paintings in situ,keeping the connection to their historical context. However, the conservation of the paintings might prove to be very difficult or impossible because of the hard to control the indoor climate conditions in the fort. A stable and controllable indoor climate is needed to prevent further degradation and the paintings should be consolidated to prevent further loss. Many paintings are damaged or lost to a great extent or have not been uncovered fully. Enough budget and time are needed to treat the problems and restore the building and paintings. To be able to preserve the paintings,

enough interest and financial options are needed. It is not likely that the wall paintings can be removed in a strappo method, which has been used on fresco paintings in the past, because of the absence of a thick stucco layer.

In general it is clear that if an interested support base for the fort is not found and preventive measurements are not taken, the fort and the wall paintings will degrade further, resulting in the loss of important cultural heritage. A new function for the fort can, on the one hand, be seen as a possible endangering factor for the preservation of the fort and wall paintings, because of changes, but on the other hand it can create a renewed interest in the fort as a whole, resulting in possibly more interest in the paintings and the generation of an income to create a sustainable future for the fort.

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Chapter 3: Architectural paint research in room 23

3.1 Introduction room 23

In order to test the use of Blender for Fort benoorden Spaarndam, architectural paint research has been carried out in room 23. Architectural paint research is the area of research in which the historical layer buildup of an object (such as an object, a room or a whole building) is studied. The aim of this research was to create an overview of the different layers present in room 23 and to connect these to the different phases of use of the fort. Because of the size of this thesis, this research has been limited to one room. In the future it might be possible to do architectural paint research within the whole fort and create a model of the complete fort. Room 23 has been selected as the pilot case study to carry out

architectural paint research and for the creation of the 3D-model. This room was chosen because of its high amount of different kinds of drawings and paintings and its accessibility during the investigation. This room has the same shape as most of the rooms in the fort, and the large amount of paintings makes it representable for most of the rooms in the fort.

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27 Room 23 is located in the main building, next to the

central hallway (fig. 28). Connecting room 23 and the hallway are smaller spaces, used as storage space and toilets. It is, like most of the rooms in the fort, a rectangular shape with a vaulted ceiling. This room is described on the map of the fort as the hospital room and consisted of two separate areas, the ‘Ziekenlokaal’ (23a) and the ‘Verbandplaats’ (23b) (fig. 28) As indicated on the image, two walls had been used to create a division from the small

hallway and within the room. These walls have been lost but are thought to be similarly to walls that are still present in room 20 and 21 (fig. 29). These rooms were meant for high ranked officials, who got more ‘luxuries’, such as more privacy and a wooden floor. Room 21 still contains this division, showing how this division might have looked for room 23.

Currently, room 23 has a concrete floor, but it is possible that it had a wooden floor similar to room 20, because of the more special function of the room. The hospital room as visible in Fort aan den Ham contains a wooden floor in part of the room (fig. 30 and 31.), so it is possible that this has also been the case in this fort.

Figure 30 Hospital room at Fort aan den Ham. Source: https://www.fortaandenham.nl/cms/fort-rondleiding/

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28 Figure 31 Hospital room Fort aan den Ham. Source: https://www.fortaandenham.nl/cms/fort-rondleiding/

3.2 Research techniques

To get a better insight in the layer build-up of the room different research techniques have been used and the results of this research will be summarized in the following chapter. First, the room was documented by taking photographs and measurements. Already present damages were studied with a Dinolite microscope camera, to gain a better insight in the layer build-up. Next to that, stratigraphies were made by scraping layers of paint off with a scalpel, to create an overview of the present layers. However, this was very difficult because of the bad condition of the paint layers, resulting in delamination and flaking of the paint layers. Because of this, creating color-steps in which all layers were clearly visible was not possible on every wall. An overview of the stratigraphies has been included in appendix 3. To help interpret the layers found during this step, samples were taken from different locations (as indicated in appendix 4..). The aim was to study cross-sections of these samples under a microscope and possibly do SEM-EDX analysis. However, this research has been limited due to the restrictions imposed by the Covid-19 outbreak. This has resulted in that only 3 of the taken samples have been embedded and studied, with help of Luc Megens (RCE) (appendix. 5).44 Because of this small amount of samples that could be studied, the interpretation of the layer build-up is based mostly on the stratigraphies. Seeing the layer build-up under the microscope can show things that cannot be seen by the naked eye and analyzing the different pigments present can tell a lot about the paint used and helps date the

44 Due to the restrictions imposed by Covid-19, the samples taken at the fort could not be embedded and analyzed under a microscope. Luc Megens (RCE) was able to analyze 3 samples.

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29 paint layer. Because of this, it could be that some layers have not been found during the creation of the color steps. However, the remaining samples might be researched in the future and the results can be adjusted accordingly.

3.3 Results of sample analysis

The sample analysis carried out by Luc Megens, SEM. This research has been included in appendix 5. Sample analysis was carried out for the following samples: B1, B2 and B7. The aim was to get an overview of the layer build-up of the upper, middle and lower part of this wall.

Figure 32 Overview of sample locations Wall B (south wall). Source: Author

Sample B1 (fig.33)

This sample shows at least three and possibly more white chalk-layers which are followed by a light blue chalk-layer with probably synthetic ultramarine blue pigment (layers 1-4). This is followed by again three or four white chalk-layers (layers 5-8).

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30

Sample B2 (fig. 34 and 35)

This sample has been taken from the area where the upper part of the wall and the lower part meet, where the black and blue lines have been applied. Because of possible overlap between these paint layers, it was expected that multiple layers were visible in the sample originating from the same phase.

The sample has split in two parts. Fig.42 shows the lower layers of the sample. First a white chalk layer is visible, followed by a light blue chalk-layer (similar to the blue layer 4 of sample B1). This is followed by a grey chalk-layer containing organic black pigment. The next layer is a thin dark blue layer with synthetic ultramarine pigment, with a very thin white chalk-layer on top. A grey chalk-chalk-layer is visible as the top chalk-layer in this part of the sample.

Fig. 41 shows the upper part of the sample. First, a light blue chalk-layer is visible, followed by a thin black paint layer. Thirdly a white chalk-layer is visible after which two grey layers follow. It is thought that the white and light blue layers of the first part of the sample relate to the layers as found in the stratigraphies of the upper part of the wall. The following grey and blue layers could be the from the third phase (see table 1). The next grey and light-blue layers, together with the black paint layer, probably relate to the fourth phase (with the stenciled decoration, see table 1.)

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31 Figure 34 Cross-section of the upper part of sample B2 (was

first upside down). Source: Luc Megens, RCE.

Figure 35 Cross-section of the bottom part of sample B2 (was first upside down). Source: Luc Megens, RCE.

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32

Sample B7 (fig. 36 and 37)

On a white chalk-layer follow two grey layers containing organic black pigment (layers 1-3). This is followed by blue layer (layer 4), made up of chalk and synthetic ultramarine (similar to layer 4 in sample B2.). After this comes a grey layer (no. 5) and a thin white chalk-layer (no. 6), followed by two grey layers (no. 7 and 8).

This analysis has shown that the build-up of the upper part of the wall is relatively simple, only containing white layers and one light blue layer. The lower part of the wall contains a white layer that was probably a preparatory layer. The second layer, a grey, can be regarded as the first finishing layer.

Figure 36 Sample B7, upper part. Source: Luc Megens, RCE.

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3.4 Results of stratigraphies

The stratigraphies have been created on different walls and in different areas of the wall, to find out if there are differences in paint layers between the layers and within the walls. The decorative schemes seem to have been limited to 23b. 23a has been kept more sober and is similar in layer buildup to the hallway, as visible in a stratigraphy made in the hallway (fig. 38). The upper half of the wall only contained white paint layers, while the bottom half of the wall contains white and grey paint layers. The first layer found is white, which might have been a preparatory layer but could have been used as the first phase. This is followed by a dark grey layer, possibly to give the impression of a wainscoting. Then follows another white (possibly a preparatory) layer, followed by two grey layers. This area probably has not been altered a lot over time and does not seem to contain decorations.

Figure 38. stratigraphy in hallway, photo: author

Room 23b contains more paint layers than 23a, so it is not completely clear how these phases relate to the ones found in 23b. It was found that the layer build-up of the three walls in 23b was very similar, with the exception of the north-eastern wall (wall D), which contains less layers. These layers have probably been lost due to water damage. A small area on this wall still contains the blue used in the decorative stenciling, indicating that this wall has also contained the same paint layers as the other walls. Because of this, this wall will be regarded in the same way as the other walls. The wooden wall dividing 23a and 23b has been lost, so it is unclear if the paint layers found on the concrete walls have been used here as well. A difference in paint layers between the upper part of the wall and the lower part has been found for most of the phases in room 23b, creating a division of the wall or the indication of a wainscoting. This makes relating the paint layers found on the upper and lower parts of the wall more difficult, because certain areas could have been overpainted more often. The

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34 upper part of the wall is relatively simple. The cross-sections of the samples and the

stratigraphies indicate that five different decorative phases have been present. A preparatory chalk-white layer has been applied on top of the grainy concrete wall. This could have been one thick layer or multiple thinner ones that are hard to distinguish. One white layer has been part of a decorative phase, because the wall paintings have been applied on this layer.

This white layer is followed by a light blue layer, which has been the second paint scheme. This blue layer has not been found everywhere, it has not been applied in the door-niche (fig. 40). In Strat. A-2 it has also not been found, even though it is clearly visible in the lacunae further to the left. This layer seems to have been painted around the wall paintings, allowing them to stay visible. It could be possible that the blue has not been applied to the edges of the wall, resulting in it not being visible in strat. A-2. On top of this blue layer follow at least three or more white layers (fig.41)

The height of the lower half of the wall has changed over time. In the most recent phase, the white upper

half of the wall is connected to a grey wainscoting, which is around 110 centimeters high. Stratigraphies indicate that multiple white preparatory layers have been applied here as well, one also possible could have been part of a paint scheme (fig. 40). This is followed by a light grey layer. Following this grey layer follows an indigo blue field. At the top of this, a grey border is found, which is placed within two dark ultramarine lines. A 15-centimeter-high border in this color has also been found located at the bottom of the wall. The third paint scheme that has been found is the stenciled decoration of a geometric flower motive in different shades of blue, placed on a grey background (fig. 42). At the height of the upper dark blue line of the previous phase, a similar black line has been painted. Phases 4 and 5 are a relatively simple dark grey wainscoting. The first of these grey layers has a more grainy texture and has less coverage than the second grey layer. The following grey layer, which is the most recent layer, has better coverage and is applied slightly higher than the previous layer.

Stratigraphies on the ceiling have shown that here mostly white layers have been used. However, a light blue color similar to the one on the walls has been found here, together with a orange layer. This orange layer has only been applied locally near the

slogans and is though to be part of this decoration. Due to time constraint, color research into the paint layers on the doors and windows has not been included.

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35 Figure 40 Stratigraphy A-5 in door-niche, East wall.

Source: author. Figure 41 Stratigraphy A-4, east wall. Source: author.

Figure 42 Wall B, south wall. Source: Author.

Figure 43 Stratigraphy on ceiling, above wall D (north wall). Source: Author.

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36

3.5 Dating of the layers

Dating the paint layers found is difficult because of the relatively young age of the building and the lack of documentation of military buildings. The dating of the decorative paint schemes is an interpretation, linked to the known phases of use of the fort. Layers could have been in use for a longer time or replaced quickly. Next to this, previous paint layers could have been removed before new ones were applied or damages were overpainted, which could also result in differences in layer build-up of the four walls. However, it is likely that changes in the paint layers relate to change in the occupation and use of the fort. This has been included in table 1.

The first colored phase, which is quite sober, probably relates to the first use period of use of the fort, after the build has been completed. The wall paintings have probably been added to this when the fort became occupied during the mobilization. There are multiple indications that the wall paintings and decorations have been part of an organized decoration plan or that it at least had been approved by the officials of the fort. First, the prominent placement and size of the many paintings and drawings in the fort seems to support this idea. It is unlikely that paintings on this scale were done in a way that was not approved by the fort commanders. Next to that, the light blue paint layer (of the second phase) does not cover the paintings in room 23, indicating that they were on display during multiple phases and were thus approved and enjoyed. Thirdly, it is known that different committees were active during both World Wars that aimed at providing opportunities for development and recreation for the soldiers stationed at the forts, which could have resulted in the decoration of the fort. These committees worked in consultation with a national committee called the Centrale Commissie voor Ontwikkeling en Ontspanning der Gemobiliseerde Troepen, which ensured that the fort commanders stimulated these activities.45 These committees not only organized physical training (see fig. 44) and educational courses, but also provided material for relaxation, for example by organizing ‘ontspanningsavonden’ with board games, theater and musical performances, carried out by both professionals and recruited soldiers. Next to these activities, sources also mention that the Committee organized arts and crafts related activities (‘Huisvlijt’), which were exhibited in the Hague (fig. 45) and ordered several rooms to be decorated with furniture and ‘gezelliger aankleeding’ as well.46 This makes it possible

45 Kooiman and C.J. Snijders. De Nederlandsche strijdmacht en hare mobilisatie in het jaar 1914

(Muusses, 1924), 347.

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37 that decoration of Fort Benoorden with paintings was done during this time, possibly as part of organized or stimulated activities.

The Commissie voor Ontwikkeling en Ontspanning was also active during World War Two, organizing similar activities.47 It is possible that one of the decorative phases following the paintings, either the phase with different shades of blue or the stencil decoration, was applied during this mobilization. Similar decorated borders have been found in Fort aan den Ham and have been present in Fort bezuiden Spaarndam as well (see chapter 1.6.)

indicating that decoration of the forts was more common and makes it even more probable that this was carried out in an organized way within different forts. 48 The fort was in use by Dutch soldiers for a longer time during the First World War than during the Second, so it is likely that the blue paint scheme dates from later in the First World War or the Interbellum. During the mobilization of the Second World War, the stencilling decoration might have been applied. However, dating the stencil decorations is difficult, because the use of stenciling was popular for a long time.

The slogans on the ceiling have probably been applied during one of the first phases of use as well, because they refer to the use of the fort. The two slogans in room 23 relate to its function as a hospital room. One slogan is: “Early to bed and early to rise keeps a man healthy, wealthy and wise”, an old proverb referring to importance of rest, meant to inspire the soldiers in the hospital room. The other slogan has not been uncovered completely, but can be recognized as a version of the oath of Hippocrates, which is known in different versions and has been related to medicine.49 The version on the ceiling in room 23 is

probably something like: “De geneeskunst is lang, het leven kort, de gelegenheid is vluchtig, de proefneming hachelijk en het oordeel moeilijk.”

47 “Ontwikkeling en Ontspanning tijdens de mobilisatie” , Oorlogsbronnen, accessed 20-07-2020.

https://www.oorlogsbronnen.nl/nieuws/bron-uitgelicht-%E2%80%98ontwikkeling-en-ontspanning%E2%80%99-tijdens-de-mobilisatie

48 Blogpost 2 January 2013, Fort aan den Ham, accessed 21-08-2020,

https://www.fortaandenham.nl/cms/blog/page/6/.

49 Oath of Hippocrates, Historiek.net, accessed 01-08-2020,

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38 Figure 44 ‘Het werk van O. en O., hoe men kruit droog moet houden’ (Bron: Beeldbank WO2, Collectie NIOD, beeldnummer 42354)

Figure 45 Huisvlijt tentoonstelling in Den Haag, 1917. Source: Nationaal Archief

Lastly, another way of dating the paint layers is by looking at the signatures that have been uncovered. Within the fort, multiple signatures were found, dating from different phases. Most of the signatures date from the 1950s, but also signatures from 1940 have been found on a door, dated 17 May 1940, indicating that a few Dutch soldiers were still stationed at the fort after the capitulation of 14 May, while waiting for further instructions.50 In room 23, multiple signatures have been found. One of the paintings has been signed G.K., while next to another painting this monogram has been written out. However, due to paint loss, this signature is hard to read (possibly G. Kottong, Kortong or Ketting. It is possible that more of the paintings in this room have been painted by G.K as well. Next to the signed paintings, three individual signatures have been written on the walls, visible on the current paint layer. Two signatures are by W. Roelands and one is by G. Tomhout/Tamhout, stating their ranks in the navy. Roelands signature is dated 18 December 1956, which falls within the period that the fort was in use by the navy as a storage space, so it makes the most sense that both

50 Wijnen, Muurschilderingen en Decoraties, 36. Zie afbeeldingen p103 van bijlage met overzicht van

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39 Roelands’ and Tomhout’s signatures were placed around this time. The ‘vloerbelasting’ signs that are still visible can also be linked to the use by the navy. This indicates that the walls have not been overpainted since the fort has been used by the navy, between 1948 and 1970.

Table 1. Overview of decorative phases and phases of use.

Phase Area Colors Period of use Date

Phase 1 Upper half White (+

paintings) First phase of use Paintings possibly from during mobilization for WW1. 1901-1913 1913-1922

Lower half Grey

Phase 2 Upper half Light blue applied around the paintings Probably mobilization WW1 1913-1922

Lower half Dark blue with grey part in between

ultramarine lines Phase 3 Upper half Possibly still blue

or white

Mobilization /WW2

1922-1940 1940-1945 Lower half Stenciled

decorations on grey background. Black line in between upper and lower half of the wall.

Phase 4 Upper half White After WW2 1948-1970

Lower half Grey

Phase 5 Upper half White After WW2

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40

Chapter 4: 3D modelling technology

3D modelling has been in development since the 1970s but gained popularity since the 1990s, within different fields such as engineering, architecture and animation for movie and games. These different fields make use of 3D technology in different ways, and thus have different requirements for their models. The development of 3D technology in these fields has resulted in a wide variety of possibilities created by 3D technology, with different characteristics, equipment, price ranges and uses. All 3D models are based on data, which can either be acquired in a reality based way or through ‘nonreal’ approaches. Reality-based techniques make use of hardware and software to record reality and create a 3D model from real measurements, such as laser-scanners and structured light scanners. Nonreal

approaches are based on computer graphic software or procedural modelling, where the 3D model that is being created is not based on metric results.51 The use of photogrammetry or modelling programs such as Blender fall into this category. The different data-acquisition techniques are discussed below.

4.1 Laser-scanning

One of the most common ways of actively collecting data for a 3D-model is by scanning an object with lasers. The scanner emits a laser point and then records the returning laser with a sensor. The distance to object is either measured through a ‘time-of-flight’ technique which calculates the distance based on the time it takes for the laser to return (fig. 47), or through trigonometric triangulation, in which the reflection angle or intensity of the returning laser indicates the distance to the object (fig.46).52 The final product consists of "a cloud” of

measurement points. These point clouds can be translated into a measurable 3D depiction of the scanned object, through computer software.53

These scanners can acquire reliable data from a range of a few centimeters up to a few kilometers, depending on the environmental characteristics and the properties of the surface and can be used on different types of equipment, such as tripods, but also moving cars, drones and airplanes. The scanner needs to record the object from different angles, so either the object or the scanner should be moved to acquire reliable data. The acquired data often needs to be ‘cleaned up’ through computer software, to remove errors, noise reduction and fill data gaps.54

51 Fabio Remondino, “Advanced 3D Recording Techniques for the Digital Documentation and

Conservation of Heritage Sites and Objects,” Change Over Time 1, no. 2 (2011): 201.

52 “Laser 3D scanner vs structured light 3D scanner”, 3dnatives, accessed 20-07-2020.

https://www.3dnatives.com/en/laser-3d-scanner-vs-structured-light-3d-scanner-080820194/#!

53 Karen E. Hughes and Elizabeth I. Louden,‘Bridging the Gap: Using 3-D Laser Scanning in Historic

Building Documentation,’ APT Bulletin 36, nr. 2–3 (2005): 37.

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41 Figure 46 Time-of-flight laser scanner principle (Van Genechten et al., 2008)

Figure 47 https://eastcoastmetrology.com/resources/applications/the-uses-and-deployment-of-large-volume-laser-scanning/

4.2 Structured Light Scanning

Similarly to laser scanners, Structured Light Scanning also works with triangulation

calculations. This technique consists of a light pattern which is projected onto an object (fig. 48). While the object or the light source moves, the pattern is distorted according to the three-dimensionality of the object, indicating its shape. A sensor or special camera can

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42 register these changes in the pattern and calculate the location of the object based on

measurements of the angle and distance between the light source, sensors and the object, translating it into point data. Software is used to create a 3D model based on this data.55 Because the camera can register multiple points at the same time, it works faster than laser scanners, which often only record one laser.

Figure 48 https://matterandform.net/blog/how-do-3d-scanners-work

4.3 Photogrammetry

Another popular way of creating 3D models is the use of photogrammetry. This is a

technique that uses digital photographs to create a 3D model, usually based on a technique called Structure from Motion. The object is recorded by a moving sensor, often a camera, taking 2D images (fig. 49). To create a 3D-model, many images of an area or object with a high degree of overlap are needed, taken from different angles but preferably with similar lighting and settings. Computer software can identify matching features in these images and create a point cloud of x, y, and z coordinates based on triangulation to calculate the three-dimensionality of the object.56 It delivers image data that require a mathematical formulation to transform the two-dimensional image measurements into three-dimensional information.57

55 “Laser 3D scanner vs structured light 3D scanner”, 3dnatives, accessed 20-07-2020.

https://www.3dnatives.com/en/laser-3d-scanner-vs-structured-light-3d-scanner-080820194/#!

56 “Structure from Motion”, Humboldt State University,

http://gsp.humboldt.edu/OLM/Courses/GSP_216_Online/lesson8-2/SfM.html

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43 Figure 49 Conceptual visualization of SfM (from Thormählen et al. 2010).

4.4 3D modelling programs

Lastly, it is also possible to create a 3D-model without the presence of an object. To do this, an object is modelled by hand in a modelling program. In this case, not the object itself is a source for the collected data, but secondary sources such as images, drawings, descriptions and similar objects are interpreted and used to construct a model in a modeling program. This way, the 3D model is not based on realistic recording and metric results but is created by hand. Different computer graphics software is available for this, such as 3Ds Max, Maya, SketchUp and Blender (fig.50)58 These programs work in similar ways, but each have their own specialties, interfaces and price ranges. 3Ds Max and Maya have been developed by Autodesk and are available for around 2200 euros a year.59 SketchUp is mostly used for digital drawing, focused on architecture and is available in different forms, ranging from around 270 to 1100 euros a year.60 Blender is based on open source development and is

available for download for free, making it a more accessible option compared to the other modelling programs.61

Figure 50

https://www.3dnatives.com/en/blender-3d-printing-020320204/

58 Remondino, “Advanced 3D Recording techniques”, 201. 59 Maya, Autodesk, accessed 20-07-2020.

https://www.autodesk.nl/products/maya/overview?support=ADVANCED&plc=MAYA&term=1-YEAR&quantity=1#internal-link-buy

60 Overview prices, SketchUp, accessed

20-07-2020,https://www.sketchup.nl/kopen/commerciele-prijzen#overzicht

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Chapter 5: Modelling process in Blender

A 3D model has been created in Blender 2.8 to test the use of the modelling program for the case of Fort benoorden Spaarndam and to compare it to other modelling techniques, as will be discussed in chapter 6. Blender is a modelling program that is available on the internet for free. It is an open source developed program, which means it is constantly being developed and improved. Some instruction and practice is needed to understand the program and the different tools, however it is a program that is generally easy to use, making it a very useful tool for cultural heritage professionals without a background in 3D technology. Tutorials or informational websites for additional explanations for Blender are widely available online as well.

The 3D model created is a reconstruction of room 23 (as discussed in chapter 3) in which architectural paint research has been carried out. The aim of this model was to document the current state of the room and to visualize the different decorative paint schemes as found during the architectural paint research.

First, the room has been modeled based upon the measurements taken in situ, resulting in a polygon mesh of a rectangular room. The basic shape of the room has been copied to create multiple objects in which the decorative paint schemes (and variations on the possibilities) have been visualized. The roof, doors and windows have been created as separate objects to make the modelling process easier.

The first model shows the room in its current state, based on photographs taken in situ. These photographs have been incorporated in the model by adding them as ‘material’ to the faces of the mesh and unwrapping them on the model. For this step it is important to make sure the different vertices align with certain locations on the images, to make the image fit to the model exactly. If this is done incorrectly it could cause distortions in the image.

The decorative paint phases have been reconstructed in the models by adding colors as ‘material’ as well (see fig. 53-56). The colors in the room have been compared to NCS color fans during architectural paint research, resulting in a color code. This has later been translated into HEX color codes, because it could be used more easily in Blender. In this way, the color is being displayed in the model in a relatively flat way, because there is no influence from texture, reflection or discolorations within the paint, making it look less realistic. This could be improved by adding a simple concrete texture on the mesh, adding characteristics to the material such as reflection or by using different light sources in the final rendering of the model.

To show how digitally restored images could be used in the model, photographs of the wall paintings in room 23 have been digitally retouched and enhanced in Gimp, a free

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