Eggshell in Artistic and Alchemical Recipes: Late Antiquity to 1800

(1)

MA Thesis

Timothy Greening

Student number: 11701706

Conservation and Restoration, specialization Technical Art History

University of Amsterdam, Amsterdam

Thesis supervisor: Dhr. dr. A.R. de Koomen

Second reader: Dhr. dr. H. den Otter

21 June 2019

(2)

Greening, University of Amsterdam 2019 1

Acknowledgements

First, I would like to thank Arjan de Koomen for his supervision of this thesis.

Thank you also to my instructors Maartje Stols-Witlox, Erma Hermans, Rene Peschar, Maarten van Bommel, Ella Hendricks and Abbie Vandivere.

I would also like to thank Herman den Otter for being the second reader of this thesis. A deep thanks is due to my family for their support, without which this thesis could not have happened.

Secondly, a thank you is due to all my C&R classmates for their comradery and support over the two years. In addition, I greatly appreciate Karina Foppele and Suzanne Bul for taking the time to send some eggshell recipes to me, in translation from Dutch. An additional thank you goes to Julia Wagner for help with some German text interpretation. Also, a thanks to Marieke Hendriksen from the ArtTechne project for some thoughts about alchemy and kilns. I would also like to thank Professor Lawrence Principe at Johns Hopkins University for the comments about alchemical calcination. Finally, a special thanks to Maria Jose Moreno, for the tea breaks and moral support.

(4)

3

Summaries

English

In technical art history, historic recipes are an important documentary source for the study of the history of materials. Investigating these recipes can provide insight into both artistic and non-artistic reasons for the choices of ingredients in the past. This thesis aims to investigate the non-artistic reasons for the use of eggshells in artistic recipes in European documentary sources from the 15th_-18th

centuries. Although eggshells have been documented in secondary sources, no one has fully traced the history of eggshell as a material in art. This thesis further explores how alchemy was a significant factor in bringing eggshells to the artistic recipe repertoire. In particular, eggshells in recipes are often burnt to create lime, an ingredient often used by alchemists. Chapter 1 outlines the material history of the calcium carbonate group of pigments, and shows how eggshells chemically belong in that category. This helps in understanding how eggshells and chalk are in fact interchangeable as a raw material. A history of historic recipe sources that reference eggshells is outlined in Chapter 2. Chapter 3 describes how the alchemists burnt eggshells in the process of calcination, by investigating

alchemical illustrations and text sources. In fact, the burning of eggshells to make lime goes back to Arabic and Greek alchemical sources. Of great interest is the fact that today’s scientists are again making lime for technical applications from eggshells, as a green technology. This enables us to use modern scientific research data on eggshell lime to help us understand the alchemist’s reasoning for making it. Chapter 4 describes the symbolic reasons why eggshell would be an important material to alchemists, again making use of alchemical illustration. This helps us understand why eggs, and chicken eggs in particular, were used in these recipes. Also, scientific research today investigates other birds’ eggs as a lime source, so the alchemical recipe assertions can be tested. Finally, a comparative review of alchemical and artistic recipes makes up Chapter 5. These comparisons show that alchemy did have a lasting impact on the choice of eggshell lime in recipes. This concludes the history of eggshell in artist’s recipes, as it relates to alchemical recipes.

(5)

4

Nederlands

In de technische kunstgeschiedenis zijn historische recepten een belangrijke documentatiebron voor de studie van de geschiedenis van materialen. Onderzoek naar deze recepten kan inzicht geven in zowel artistieke als niet-artistieke redenen voor de keuzes van ingrediënten in het verleden. Deze scriptie onderzoekt de niet-artistieke redenen voor het gebruik van eierschalen in artistieke recepten in Europese documentatiebronnen uit de 15e-18e eeuw. Hoewel eierschalen in secundaire bronnen zijn gedocumenteerd, heeft niemand de geschiedenis van de eischaal als materiaal in de kunst volledig in kaart gebracht. Deze scriptie onderzoekt verder hoe alchemie een belangrijke factor was bij het incorporeren van eierschalen binnen het artistieke receptenrepertoire. In het bijzonder worden eierschalen in recepten dikwijls verbrand om kalk te maken, een ingrediënt dat veelvuldig door alchemisten wordt gebruikt. Hoofdstuk 1 schetst de materiaalgeschiedenis van de

calciumcarbonaatgroep van pigmenten en laat zien hoe eierschalen chemisch in die categorie passen. Dit helpt om te begrijpen hoe eierschalen en krijt in feite uitwisselbaar zijn als grondstof. Een

geschiedenis van historische receptbronnen die verwijzen naar eierschalen wordt beschreven in hoofdstuk 2. Hoofdstuk 3 beschrijft hoe de alchemisten eierschalen verbrandden tijdens het calcineren, door alchemistische illustraties en tekstbronnen te onderzoeken. In feite voert het verbranden van eierschalen om kalk te maken terug naar Arabische en Griekse alchemistische bronnen. Van groot belang is het feit dat de hedendaagse wetenschappers opnieuw kalk maken van eierschalen, als een groene technologie voor technische toepassingen. Dit stelt ons in staat om moderne wetenschappelijke onderzoeksgegevens over eierschaalkalk te gebruiken om ons de alchimistische redenering voor het maken ervan inzzichtelijker te maken. Hoofdstuk 4 beschrijft de symbolische redenen waarom eierschaal een belangrijk materiaal zou zijn voor alchemisten, wederom gebruik makend van alchemistische illustraties. Dit helpt ons te begrijpen waarom eieren en in het bijzonder kippeneieren in deze recepten werden gebruikt. Ook onderzoekt de moderne wetenschap onderzoek de eieren van andere vogels als kalkbron,waardoor de beweringen in de alchemistische receptuur kunnen worde2n getest. Ten slotte vormt hoofdstuk 5, een vergelijkende beoordeling van alchemistische en artistieke recepten. Deze vergelijkingen tonen aan dat alchemie een blijvende invloed heeft gehad op de keuze van eierschaalkalk in recepten. Hiermee wordt de geschiedenis van eierschaal in kunstenaarsrecepten van de kunstenaar afgesloten, aangezien deze betrekking heeft op alchemistische recepten.

(6)

5

Introduction

To most of us only a waste product in the kitchen, the eggshell has an interesting place in the history of art technology and alchemy that can be traced to late antiquity. Eggshells have a wide variety of uses in the recipe literature. The recipes are diverse and are not only for white painting pigment, but other artistic applications. These recipes seem to be using eggshell to whiten the product, acting as if it was chalk. This use can also be found in other recipes where eggshells function with a dye, like brazilwood, to make a coloured product; in essence, this is a colourant made from dyed eggshell, known as lake. Also, by the 18th_{century there are several ‘eggshell white’ pigment recipes where the}

eggshell functions simply as a white pigment. However, the most frequent use of eggshells is to make lime, also described as burnt eggshells or calx. This in turn is used in 15th_{century recipes for lime blue}

(synthetic copper blue), as an improvement to previous lime blue recipes that took months to make. With this diversity of uses, eggshell appears to have an important role in artistic recipes which needs to be further explored. The other place in history where eggshells have a use is in alchemical practice. What is more, is that the use of eggshells in the alchemical corpus is specified to be as calx.

Therefore, it seems that this substance is more than just a substitute for chalk. Ideally any

explanations of these observations should also have scientific validity. To this end, this thesis explores the connection between these artistic recipes and alchemical references to eggshells.

Rational: While researching the pigments of Japanese art, this topic revealed itself, despite that they

do not at first seem to relate. Sample books are a part of art technological research generally, and the Rijksmuseum library has a publication with pigment samples in Japanese art included in an appendix.1

This includes samples of coral pink, lead white, and oyster shell white (the latter apparently being the most popular white in Japan, possibly because Japan is an island). This leaves the reader wondering whether or not seashell-based whites were popular in European art history. However, my literature survey showed that references to eggshells, and instructions as to their use appeared far more frequently than references to sea shells, but chalk remains a significant white material in the art history of Europe.

Approach: An important question to ask when approaching art historical research from a technical

angle is: How was art made in the past? Answering the question can be helped by the fact that artist’s recipes have been written for a long time. So, in this thesis, what will be analyzed is recipe text. How will the text of recipes be analyzed? First, the artistic texts can be compared to other historical literature, as well as alchemical documents. Next, we will look at historic alchemical illustrations of two key components of the recipes; the use of chicken eggs and calcination. Finally, modern research into eggshell calcination will be investigated to better understand the thought process behind the alchemical and artistic practices of the past. Since modern researchers are already calcining eggshell, and publishing scientific results about it, performing reconstructions of actual lime recipes for this thesis seemed redundant.

(7)

6

Research Question/Sub-questions: Why would an artist or colourman process eggshells by burning to

make pigments, when there are many other ways to acquire lime?

Since the alchemists treat eggshells in the same way, we can ask a series of sub-questions: Are alchemists the reason for this ingredient to become part of practice? What reasons did alchemists have for developing their own eggshell recipe practice? When did eggshells enter recipe literature? Finally, since alchemy was the beginnings of the modern concept of chemistry, we will investigate the following: How sound is the science behind the decisions to include this ingredient in recipes?

Place within Technical Art History

To investigate the history of eggshells in art history is a challenging undertaking, as in involves materials science and alchemical history as well as art technological source research. This is why technical art history (TAH) is an ideal discipline to tackle this problem as it works at the intersections of art history and science. Although technical art history can be focused on techniques, it remains a form of history and as such, a material history can find its place in TAH as a discipline. Therefore, writing a history is the approach that will be used in this thesis. In the simplest terms, this will put emphasis on placing the pigment recipes across a broad time scale and in many locations, rather than on their artistic properties. The artistic properties will not be investigated, as it is too complex to explore all the nuances of art making within one thesis, while also writing a history. To relate this history to alchemical history is not out of place in TAH, as there are other examples of alchemical practice being used to make artist’s materials, particularly pigments, that have already been

addressed in the literature. This thesis therefore, will hopefully compliment other past TAH literature. In terms of science, TAH frequently uses scientific analysis to further understand the nature of materials of the past. In the present, research often includes the technique of reconstruction, in combination with instrumental analysis, to gain a better understanding of artistic practice. Broadly speaking, this approach necessitates the materials be made from natural raw materials to give them some historical authenticity. This thesis is different, in that it uses green technology research to offer a ‘reconstruction’ of eggshell lime. This is not ideal, since it does not directly involve art history, or alchemical history, but it has its place, which is to offer chemical information about this material. In summary, this thesis fits into the scope of the interdisciplinary field of technical art history. Its place in the discipline is to add to our understanding, not only the material of eggshell as an artist’s pigment, but also its use in relation to alchemical practice.

Background/State of the Art: The egg of the chicken is an object much studied, by many different

disciplines. This fact will aid our technical understanding of this ingredient in recipes. In addition, biologists and food industrialists are both interested in the biochemical composition of shell and its formation, as well as its thickness.

In terms of geography, this thesis is focused on Europe, with an emphasis on the northwestern portion. This would seem to be quite broad for one thesis, but overall is actually quite narrow, within this topic. For example, there was not enough room here to explore the history of chalk in Arabia, and its relation to Arabic alchemical practice, nor to consider the ancient Greek alchemical originators, and their relation to chalk in recipes. As English, German, Dutch, and Italian recipes are referenced, this is the geographical reference region for geological discussion.

(8)

7

Throughout the world pigments are a critical component of many artworks, and white, while not a colour per se, is an important pigment. It is used to create white ground to support and brighten other colours, and creating highlights and light tones. Aside from its unsuitability to make oil paint, chalk was occasionally used in painting, despite lead’s dominance in this role. So, an important question to be addressed is: What is chalk? In chemical terms, it is calcium carbonate (CaCO3),

although this mineral is widely found in nature under other names, such as marble and limestone. Shells, from marine sources or fowl, are also made of calcium carbonate. The first chapter therefore will briefly review this material, and in particular, it will discuss the chemical and mineralogical nature of the material, in a European geographical context. This will help us better understand what the materials being discussed in recipes actually are. This will be followed by a brief overview of the use of chalk as a pigment, also in a European context, as well as addressing how eggshell fits into this calcium carbonate group.

Eggshell is widely acknowledged by historians studying recipes. However, this is usually addressed by cataloguing old recipes rather than for the creation of new research questions. Also, the internet has given access to some historic artistic recipes in facsimile of the original form. This issue will be addressed properly in Chapter 2, with a focus on the book, the Liber Illuministarium.

Calcining is a well-known chemical reaction used to make lime (calcium oxide, CaO) out of calcium carbonate base materials like chalk. The book Painting Materials: A Short Encyclopedia, offers an overview of pigments globally. While focusing on oyster shells and coral’s long history in art in Japan and China, similar applications in European art are not mentioned specifically. The authors, Gettens and Stout, “suppose” the shells in Japan are burned before use.2_{Gettens and Stout also say that}

“even eggshells could be calcined to make a kind of lime white.’3_{The original sources or why it is}

surprising that “even eggshells” were used is missing from this reference. However, there should be no surprise here as calcined eggshells turn up quite frequently in the recipe literature, and are used to make pigments other than lime white. Furthermore, alchemists were also frequently referring to the calcining of eggshells. It therefore follows that further investigation of lime and alchemical calcination will help us understand why the above authors supposed the shells were burned and would express surprise that ‘even eggshells’ could be calcined. While it is true that other sources describe the use of eggshells to make pigments without first turning them into lime, the process of making lime from eggshells is a repeated feature of the literature. This will be described in detail in this thesis. Although somewhat forgotten in the Industrial Revolution, in our own ‘post-industrial’ era, there seems to be a kind of eggshell renaissance occurring that deserves more than a footnote for the discussion of artist pigments. Eggshells from food processing facilities are a large mass of waste that in a green economy could offer a value-added use in recycling. It is for this reason that there is a large amount of research into how calcium oxide (lime) could be produced from waste eggshells. As an aside, some of these researchers have even taken to waste ostrich eggshell to produce a catalyst for biodiesel production. Indeed, optimization of waste cooking oil and eggshell (chicken or

otherwise) derived lime production of biodiesel publications are a trending research field. Although

2_{R. Gettens and G. Stout, Painting Materials: A Short Encyclopedia, (New York, Dover, 1966),104.} 3_{Ibid. 104.}

(9)

8

labeled as “green chemistry” the thought of this concoction of kitchen wastes transmuting to the “black gold” of biodiesel, certainly brings to mind the alchemists of yore.

Although much studied by modern researchers there seems to be a gap in the understanding of the history of the eggshell as a material generally, and also in artistic production. For example, though many contemporary scientific articles discuss the potential of eggshell lime production, none acknowledge the fact the alchemists were working on this, centuries ago. However, the above information on this topic will enable us to answer the sub-question about the scientific validity of the alchemical recipes. This in turn will help our understanding as to why this ingredient would still be used in artistic recipes.

(10)

9

Chapter 1: Calcium Carbonate Pigment Group: Chalk, Seashell and Eggshell

Shell white is part of a larger group of white pigments, the calcium carbonate group. This group which includes chalk and synthetic precipitated chalk, are widely used in the paint industry today as whiting, and have been for a long time. Below is a brief account of the chemical compound calcium carbonate in terms of its chemistry, followed by an investigation of chalk’s place in art history and comparison to eggshells. This section is necessary to give background to the eggshell recipes, as those recipes are comparable to similar recipes that use marble dust, chalk, or travertine in place of the eggshells. Calcium carbonate (CaC03) exists chemically in two major crystal forms; calcite and aragonite. The

aragonite form is much rarer in nature as a natural mineral. There are even rarer crystalline forms of calcium carbonate represented in the minerals vaterite and ikaite. In fact, at the time of this writing another form of calcium carbonate was discovered by accident in a laboratory, and announced to the media.4_{However, since this crystal form has not yet been proven to be stable in nature, it will not be}

given a common name. Due to the chemical nature of calcium carbonate in minerals, calcite is the most common form in natural deposits regardless of their source. So, this means chalk, limestone, marble, travertine and calcitic alabaster, are mostly calcite. Egyptian alabaster is the term used to describe the calcitic form.5_{This background sets the stage for the fact, which will be discussed below,}

that eggshells are made of calcite.

However, in other biological sources, aragonite is often present. Therefore, pearls and nacre are mostly aragonite , although the distribution of this mineral in nature is varied.6_{Thus, some seashells}

are only aragonite, while others are only calcite.7_{Due to the very slightly reduced stability of}

aragonite compared to calcite on a geologic time scale, the prehistoric sea life’s aragonite is

converted into calcite in chalk or limestone by nature.8_{However, the remains of the sea life that gave}

us chalk deposits do leave tiny fossils behind in the chalk, called coccoliths. These are often used by technical art historians to identify chalk in artworks, as will be discussed below. Now we will turn our attention to chalk as a specific material and investigate its history.

Chalk History

Chalk is a material known to ancient people. In Latin it is called creta, from which other languages derived their word for chalk, such as Dutch krijt. However, Latin was unsystematic in its precise designation, creta meant any kind of white earth; clay or chalk.9_{Today we take the context of the}

classical writers to understand what they mean; creta from chalk mining regions seems to match the description of today’s chalk, but many other white minerals could be described in classical sources as creta.

4_{Max Plank Gesellschaft, “More Calcium Carbonate.” 2019.} https://www.mpg.de/12771653/chalk-calcium-carbonate-crystal-structure Accessed March 30, 2019.

5_{Gettens and Stout, Painting, 118. Gypsum alabaster (calcium sulfate) is also used in art history, but the finer} details of this history are out of the scope of this thesis.

6_{N.a. “The Mineral Aragonite” 2019.}_{https://www.minerals.net/mineral/aragonite.aspx}_{Accessed May 3, 2019.} 7_{R. Gettens, E. West-Fitzhugh, and R Feller, “Calcium Carbonate Whites” Studies in Conservation, 19, No.3,} (1974), 157-184. 166.

8_{Gettens, West-Fitzhugh, and Feller, “Calcium”, 166.} 9_{The Oxford Latin Dictionary, 1982 ed. s.v. “Creata”}

(11)

10

The material chalk is too widely used for a complete history of its use in art to be described here. The temporal nature of our own childhood blackboard drawings attests to the difficulty in fully

understanding man’s creative use of chalk across history. In spite of this, some have said chalk goes back to “the earliest times.”10_{At any rate it has been found, for example, in paint pigments from the}

Greek and Roman eras.11_{In other words, the exact answers to questions about how mankind learned}

to use the colour white on its own, as a support for other layers of colour, or to mix tones with other colours is lost to history. However, chalk was certainly being used as an artistic material in Europe during the late Middle Ages as will be discussed further.

In art history, two locations come to mind in the production of chalk for grounds and paint

preparation: Champagne in France, and Bologna in Italy. Also, the proverbial “white cliffs of Dover,” are strongly associated with chalk. The geography of these locations will be briefly investigated. Various technical art history literature references describe the grounds of paintings in Northern Europe generally being made with chalk, particularly in France and the Low countries.12_{This art}

historical fact matches the geological reality. Most of northwestern Europe is underlain by chalk. Today, the conservator’s supply website Kremer Pigmente and other sources still sell chalk from Belgium or the aforementioned Champagne chalk specifically for artistic purposes. These locations, and the white cliffs of Dover, are from the same deposit as described by modern geologists (Figure 1).

This deposit has given its name to the pigments Troy (Troyes) white, Rouen white and Paris white as described in the literature.13_{These individually named white pigments were thus simply local chalk or}

perhaps lead based whites adulterated with the cheaper chalk. These facts demonstrate that,

10_{Nicolas Eastaugh, The Pigment Compendium, (Taylor and Francis, London, 2008), 92.} 11_Ibid.

12_{Gettens and Stout, Painting, 104.}

(12)

11

particularly in the past, locally produced materials were the most widely used by artists at a particular location.

In Italy, the relationship between artists and chalk is quite different. It is interesting to discover that Bologna “chalk” contains gypsum. Although sources are slightly conflicted as to whether or not it is pure gypsum, some gypsum is always present. Even today, the conservator’s supply website Kremer Pigmente offers the product “Chalk- from Bologna”; which according to the MSDS sheet is a natural mixture of calcium sulfate (gypsum) and calcium carbonate.14_{This is not surprising as gypsum is}

mined in the Bologna region, to this very day (Figure 2). Travertine and marble are two calcium carbonate minerals found in Italy, and occur in Italian artistic recipes, in powdered form. Then there is gypsum, or gesso in Italian, which has its own history of use in art. The lack of references to eggshells in Italian recipes will discussed later.

Chalk is usually found in the ground layer of northern European polychrome sculpture, and this also goes back in time. Studies of Norwegian polychromy identified chalk in the ground layer, where chalk is not native. Using microscopic fossil studies, it was found that between 1100-1250 chalk for

polychrome ground was imported from England.15_{Later, chalk came from France. This means that, by}

1100 chalk was being shipped as a commodity, and used for artistic purposes. Another artistic use of chalk, which goes back to the Middle Ages, was to precipitate lake dyes made from organic colourants like brazilwood to be used as pigments. In many recipes, this is accomplished by using powdered chalk. In England, however, dye solution was poured into a hollow made in a solid block of chalk, and

14_{Chalk from Bologna, Italy, MSDS No. 58100 (Online); Kremer Pigmente, Aichstetten, Apr. 3, 2003.} https://shop.kremerpigments.com/media/pdf/58100-58150MSDS.pdf Accessed May 2, 2019.

15_{Lucretia Kargère and Adriana Rizzo “Twelfth-Century French Polychrome Sculpture in The Metropolitan} Museum of Art: Materials and Techniques”. Metropolitan Museum Studies in Art Science and Technology, 1 2010, 39-72, 43-44.

(13)

12

the lake pigment was collected out of the hollow.16_{It is no coincidence that this extravagant}

technique is from a nation known for white chalk cliffs that easily provide these blocks.

The interpretation of this information is complex. On the one hand, there is a clear geographical connection to the minerology of regions and local art recipes. The Italians, being isolated from the north by the Alps, used local material from gypsum deposits. However, there is evidence that chalk for artistic purposes was shipped even during the Middle ages. It seems that skill and human

movement would also be a factor here. Certainly, in the Middle ages the Anglo-Saxon cultural impact would be greater in Norway than Italian influences. So, chalk was moved to where it was needed; the locations where craftsmen were taught to use it. In addition, it was interesting to consider that it is not always clear what chalk actually means in historic sources, and that problem continues into our own time with Bologna chalk. This is important for the critical reading of recipes.

Calcium carbonate in eggshells

An egg is a complex biological system, and as such has been much studied in science. One study from 1996 presents a good summary diagram of what an eggshell looks like in cross section (Figure 3).

Although presenting all of the complexities the diagram shows the shell is composed of four main layers. The innermost layer, a membrane or skin gives the system a separating barrier between the egg white and shell. It is composed of collagen and other proteins. The majority of the shell adjacent to the membrane is calcium carbonate crystals in the calcite form. This is combined with palisade vessels within this mass of crystals. Between this layer of calcite and the top membrane researchers

(14)

13

have identified a thin layer of hydroxyapatite.17_{This is a calcium-phosphorus compound with the}

formulaCa5(PO4)3(OH), and the main component of human bone.18 However, the middle layer is so

much thicker than the rest of the shell, that the eggshell as a whole is mostly calcium carbonate, with only a small protein component.

In conclusion, calcium carbonate can come from many sources and is clearly influenced by local geography/geology. The placement of eggshells in the calcium carbonate group of pigments makes sense, because calcium carbonate in pigments from chalk usually comes in the mineral form of calcite. As a final note, one reference was found to research on Roman frescos where aragonite was identified spectroscopically as the white material used specifically to mix colours in the painting process. The authors do not acknowledge the possibility of shell white, but instead suggest it is a natural creta, as described above, that happened to consist of aragonite.19_{Similarly, seashells more}

often contain aragonite. As it turns out, the eggshell is a relatively pure source of calcium carbonate as calcite.

17_{J. E. Dennis, Arthur Heuer, “Microstructure of matrix and mineral components of eggshells from white} Leghorn chickens (gallus gallus)” Journal of Morphology 228 (1996), 287-306.

18_{“Hydroxylapatite” Mindat, 2019, Hudson Institute of Minerology}_{https://www.mindat.org/min-1992.html} Accessed May 25, 2019.

19_{Gian Antonio Mazzochin, Emilio Francesco Orsega, et al. “Aragonite In Roman Wall Paintings of the 8}th_Regio, Aemilia, and 10th Regio, Venetia et Histria” Annali di Chimica, 96, 2006, 377-87, 386.

(15)

14

Chapter 2: Eggshell Pigments: An Overview

Although Gettens and Stout described a kind of lime white made from eggshells, the usage of this ingredient in recipes is more diverse than as a white pigment. Several sources describe a very specific use for eggshell in art technology, which is the production of lime blue. Lime blue is a pigment used in wall painting whose exact chemical composition is still questionable, despite the advances in chemical research. Its class is in the synthetic copper blues, meant as alternatives to azurite. While many different approaches to synthesizing blue from copper (or brass) in the late Medieval period have been discussed, the one that matters to us is blue made from verdigris, sal ammoniac and lime. This has been well studied in a paper in the journal Studies in Conservation, where long list of 15th_century

sources for recipes based around this formula are discussed.20

The recipe writers working north of the Alps specify eggshell lime in recipes. Note, in Chapter 4 we will address the fact that 8th_{century Arabic alchemists used the same ingredient list in non-artistic}

recipes. However, it is also known that verdigris comes to Europe from the Arabs anyway.21_{One of}

the recipes from this list is taken from the Amberger Malerbuch, and apparently came from a Viennese source. It will be discussed in Chapter 4/Appendix I. The Italians also made this lazur pigment, but in a different way. The lime used was specified to be made from marble or travertine in two recipes, both from the Bolognese manuscript.22_{This raises the question: If the Italians knew}

about this formulation for lazur, why would they choose other lime sources over eggshells? Alchemy was certainly practiced in Italy at the start of the early modern period. However, it seems the Arab presence in Spain meant their alchemical manuscripts moved into central Europe from there more readily than into Italy.

One must mention the outlier here, a Dutch recipe from Ms Sloane 345 B, which says to use lime made from either eggshells or marble.23_{There must be a combination of German and Italian}

influences here. It thus is suggesting that the source of the lime in fact doesn’t matter. Why the Germans and Italian came to specify different sources of lime remains unknown. Later in time, other recipes can be found in the literature, besides these lime blue recipes. The book Artist Pigments c. 1600-1835 lists English language printed books that contain eggshell pigment recipes. Two of those recipes will be discussed further in Chapter 4. However, these recipes are more modern, from the 18th

century, and are for eggshell white specifically. Again, this is not the lime white described by Gettens and Stout. In summary, it seems that Gettens and Stout had a poor understanding of the role eggshell calcination played in artistic recipes. Instead of only acting as lime white, as they describe, it had a role in being prepared specifically for the production of another pigment, lime blue.

Significantly, of the nine Germanic language references to eggshell lime described in the Kreigel and Polborn tabulation of lazur recipes, five are from the same source, officially titled: Liber

20_{Christoph Krekel and Kurt Polborn, “Lime Blue- A Medieval Pigment for Wall Painting?”, Studies in}

Conservation 48 No. 3 (2003), 171-182. 175.

21_{Spansgrun (Spanish Green) in German, and verdigris (Green of Greece) from French, still indicate the Arabic} world’s influence on the introduction of this copper salt to Europe.

22_{Krekel and Polborn, “Lime Blue” 175.} 23_ibid

(16)

15

Illuministarum pro fundamentis auri et coloribus ac consimilibus collectus ex divirsis. This book will now be discussed in more detail.

Liber Illuministarum: The Tegernsee Manuscript

An important source to consider for eggshell-based pigment recipes is what is called “the Tegernsee Manuscript”, or Liber Illuministarum, the ‘book for book illuminators.’ This collection contains over 600 art technology recipes written in German and Latin.24_{One recipe from this book will be discussed}

in depth in Chapter 4; the other recipes will only briefly be reviewed here. The Tegernsee Manuscript comes to us from the Benedictine monastery in Tegernsee in Bavaria. Although founded in the middle of the 8th_{century, the monastery was sacked by Ludwig of Bavaria in 1206, then damaged by}

fire in 1206 and 1211.25_{This suggests that the recipe sources are later than this, and it appears likely}

that much information was lost. Liber Illuministarum is dated to the second half of the 15th_century

and has many recipes that are unique to it.26

Conveniently catalogued in the 2005 print edition, the index lists several recipes that use eggshell, including instructions to make eggshell lime. This substance, eggshell lime, itself in indexed separately (eiernschalenkalk), and is put to use in many of its own recipes, particularly to make the

aforementioned lazur, of which quite a few versions exist in this book. The reason that more references to lazur appear in this book than Krekel and Polborn describe in their 2003 lime blue paper, is that many of the instructions in the hundreds of pages of manuscript in this book are repetitions, or cross references within the manuscript. As described in the title, (‘A Medieval Pigment for Wall Painting?’), Krekel and Polborn’s paper explores the possibility of lazur being used as a wall painting pigment, mainly due to the expense of natural ultramarine. Evidently, lazur was also

important to the book illuminators, as is expected from the book’s title. On top of this, many a recipe using or making glair, (egg white as a painting medium/varnish/adhesive) are in this book. Glair is known to be important for traditional book makers so this further validates the book being used as instructions for book illuminators. Here it is worth mentioning that the use of glair/egg white as well as yolk (i.e. tempera) in recipes throughout the Tegernsee Manuscript suggest there was an available source of eggshells to the user.

Another recipe, somewhat unexpected uses eggshell lime (Original German aẏr kalch) with alum and brazilwood in a pigment lake.27_{It is unexpected since, as described above, chalk (not quicklime) is}

traditionally used to make lakes. However, we will see a secondary source below that suggests blue lake was made with eggshell lime and woad in 15th_{century England. In addition, there is also a recipe}

for cleaning pearls that uses quicklime (calcem viuam), egg white and calce ovorum (eggshell lime).28

Although it may not count as an artistic recipe per se, it does show that eggshell lime was seen at that time as somehow being different than ordinary quicklime.

24_{Joyce Hill Stoner, Rebecca Rushfield, Conservation of Easel Paintings, (Routledge, Oxford, 2012) 21.} 25_{“Tegernsee, Benediktinerabtei St. Quirinus”, MRFH, 2012,}_{https://www.mrfh.de/2590}_{(Accessed May 29,} 2019)

26_{Stoner, Rushfield, Conservation, 21.} 27_{Bartl, Der “Liber”, 374-5.}

(17)

16

So, in summary, eggshell was an often-used ingredient in 15th_{century recipe writing in the Germanic}

cultural area. The most important point to take away from this is the frequency at which eggshell was processed to lime. The lime becomes arguably more important than the raw eggshells itself. First, we have seen that eggshell lime was put to other uses besides lazur production. Also, a recipe is provided for making eggshell lime itself. This is important since it suggest that artists were expected to make the lime themselves.

The conclusion here is that is a lot more to eggshell calcination in recipes than the ‘kind of lime white’ referenced by Gettens and Stout. The reasons for this variety of uses will be discussed in the following chapters, beginning with an investigation of calcination in an alchemical context.

(18)

17

Chapter 3: Alchemical Calcination

Written Sources

Now we will focus the research into eggshell lime production specifically. This comes about from a comment published in the aforementioned journal article describing the synthesis of lime blue pigment:

“…Dutch or German sources describe the use of lime produced from eggshells (in their recipes). This last material indicates some connection between these recipes and alchemical laboratories, where lime from eggshells was extensively used.”29

Furthermore, the book The Pigment Compendium describes eggshells being sold as a pigment at a Munich pharmacy in the 15th_{and 16}th_centuries.30_{The product in the listing is “Calx de tistis}

ovorum”-in English, calx of shells of eggs. Calx, or lime, is what is beovorum”-ing sold here, not normal eggshells. It is worth noting that The Pigment Compendium does not note this distinction. In the lime blue recipe literature eiernschalenkalk or gebrandt eierenschalen are both referenced, and assumed to be the same thing. The choice of this Germanic salesman to use the Latin name for this product may show a connection to the manuscripts of the 15th_{century compiled in the aforementioned Liber}

Illuministarum, which mostly used Latin in the recipe instructions despite being compiled in Germany. The question as to whether eiernschalenkalk, gebrandt eierenschalen, eggshell lime and burnt

eggshells, in English and calx in Latin are always describing the same thing, seems clearly in the affirmative when one reads sets of similar recipe instructions, which use the various terms interchangeably. A more pertinent question might be, why would some writers choose

gebrandt/burnt to describe the ingredient, when it is actually something quite different? This will be discussed in more detail later in this chapter.

The book The Materials and Techniques of Medieval Painting by Daniel Thompson is a good secondary source about pigments. His references to eggshell lime include recipes where calcined marble dust or lime made from eggshells is used to make a blue pigment from waste woad dyeing solution. Unfortunately, this reference is only “a 15th_{century manuscript in Cambridge” and cannot}

be traced further.31_{The other reference in Thompson concerns the author Cennino Cennini’s}

description of calcining bones, where they are put “into the fire… until they are whiter than ashes.”32

Thompson says verdigris and orpiment were sometimes whitened with “eggshells, calcined in the same way as bones.”33_{It is again disappointing to not be able to get to primary sources from this.}

What can be said is that there are two different uses for eggshell lime are described here.

In conclusion, lime produced from eggshells evidently exists and was described in artistic recipes. As discussed in Chapter 2, most of the primary sources available today are from 15th_{century Germany,}

an historical period when lime was produced by the process of calcination at high temperatures. This

29_{Krekel and Polborn, “Lime Blue” 175.} 30_{Eastaugh, Compendium, 153.} 31_{Thompson, The Materials, 140.} 32_{Thompson, The Materials, 95.} 33_{Ibid. 96.}

(19)

18

process can be applied to almost any material, so the role of this process in alchemy will first be introduced, before a discussion of the relation between alchemists and eggs.

Use of Calcination by the Alchemists: Lime and Language

In modern thinking, calcination is the decomposition of calcium carbonate into carbon dioxide and calcium oxide, or lime, by heat. The process of calcination, from which the word calcium is derived, is ancient, as the Romans made use of lime in mortar. Calcination is an important process which has an impact on the history of pigments. Although mostly known as having a critical role in the process of buon fresco, the process to produce lime is used to produce a product that was an ingredient in pigment recipes, and was also used as white pigment in secco painting. So, the history of this process, in an alchemical context, will now be examined as it relates to the use of eggshells in pigment

manufacture.

A thought here can be given to language heritage; in English technical usage, calcium oxide, CaO, is quicklime and calcium hydroxide, Ca(OH)2 is slaked lime. Where do these terms come from? Lime is

an Old English word of Germanic origin and so relates to the Dutch lijm, and German leim.34

Linguistically they may relate to the practice of adding lime to farming soil to improve its fertility.35

Loam (a kind of light soil for farming) comes from this root, which again relates to the Dutch leem and the German lehm.36_{‘Quick’ as a preface comes from the Old English cwic, cwicu ‘alive’, which is}

distantly related to the modern English word quick.37_{This means the calcium oxide produced by}

calcination is ‘living lime’. Meanwhile, the verb to slake in English means to diminish or reduce (one’s efforts, or thirst), and has been in use since around 1000 AD.38

It is not a stretch of the imagination to put yourself in the minds of the pre-Enlightenment thinkers. Calcium oxide is quite caustic; it is “alive”, and as a “living” being it needs its thirst “slaked” with water to ‘’calm it down” and make it more useful in construction or as a surface coating. When quicklime is slaked, it swells up in volume and makes the water it is placed in boil. Also, it is worth remembering that the alchemists left this form of language on another English word; quicksilver, or mercury. The name naturally is related to mercury’s nature as the only metal that is liquid at room temperature. The Dutch and Germans retained the common Germanic stem -cwic for naming this metal, connecting it to alchemical naming. This ‘living’ silver in the English language also maintained a 12th_{century alchemical title of planetary association with metals, Mercury for the first planet in the}

34_{"lime, n.1". OED Online. March 2019. Oxford University Press.}

https://www-oed-com.proxy.uba.uva.nl:2443/view/Entry/108432?rskey=QVXTJT&result=1&isAdvanced=false (accessed May 25, 2019).

35_{"loam, n.". OED Online. March 2019. Oxford University Press.} https://www-oed-com.proxy.uba.uva.nl:2443/view/Entry/109439 (accessed May 25, 2019). 36_Ibid

37_{"quick, adj., n.1, and adv.". OED Online. March 2019. Oxford University Press.}

https://www-oed-com.proxy.uba.uva.nl:2443/view/Entry/156418?rskey=6VRLvj&result=2&isAdvanced=false (accessed May 25, 2019).

38_{"slake, v.1". OED Online. March 2019. Oxford University Press.}

(20)

19

solar system.39_{This is opposed to the Classical heritage of hydrargyrum (‘water-silver’) as the Latin}

word for mercury, which is maintained as the symbol Hg on today’s periodic table.

Now we shall give a closer look at the Latin word calx. Calx is defined in the Oxford Latin Dictionary as limestone or lime. Another Latin dictionary gives the similar definition only with the added

clarification that the lime could be slaked or unslaked.40_{The Oxford Latin Dictionary further focuses}

this word definition as pointing out that calx viva “living lime’’ is quicklime: the alchemical language heritage in English in fact draws on the classical tradition. There seems to be some confusion over what exactly calx means, as limestone and lime are two entirely different materials. However, for our purposes, ‘calx of eggshells’ could logically only be lime, or calcium oxide.

The book Cyclopædia, or, An universal dictionary of arts and sciences, by Ephraim Chambers, (1728) is an interesting source in its own right. Apparently one of the first English language encyclopedias, this offers many definitions couched often in pre-Scientific Revolution- language that can help us peer into how people thought at the turn of the 18th_{century or earlier. Calcination and related}

terminology are given an extensive article in this encyclopedia. Although there is no specific mention of eggshell lime some things described are relevant to the present discussion. “Potential calcination”, by the action of corrosives that contain “potential fire” like sal ammoniac is described as a possible process, which chemistry now knows is in no way related to the action of heat in a kiln.41_{Also the}

process of calcination is said to occur when the “… particles of fire likewise do insinuate themselves… throughout its whole substance, so that the fluidity that was first caused by the fire can no longer subsist.”42_{Again, this is not a modern scientific view of a reaction. The energy heating a substance to}

drive a chemical reaction is much more complex (and less humanized) than insinuation by particles of fire to create “a third body” after the heating process.43_{The main point to take away is that even in}

the early 18th_{century, the understanding of calcination was still quite far from the reality of modern}

laboratory processes. It is therefore quite probable it would have also been seen that way by artist’s colour makers of earlier centuries, and naturally by extension, the alchemists themselves.

In terms of putting this into the context of the research question, about processing eggshells, let us first consider that Cennini’s description of calcination is simply putting something into the fire. Furthermore, as mentioned above; why use the word gebrandt/burnt to describe this product in recipes? In his book The Tacit Dimension, British philosopher Michael Polanyi writes “we can know more than we can tell.”44_{This concept became known in academia as “tacit knowledge”, i.e. writers}

presuming (or assuming) prior knowledge of the topic from the reader in their document. The confusion between properly calcined eggshells and burnt eggshells can be explained by considering the tacit knowledge factor. In other words, there is a reason to believe that artist recipe writers presumed the reader, for example, would already know not to simply hold a piece of eggshell in a candle flame when indicating gebrandt eierenschalen as a recipe ingredient. There seems to be no

39_{"mercury, n.". OED Online. March 2019. Oxford University Press.}

https://www-oed-com.proxy.uba.uva.nl:2443/view/Entry/116711?rskey=dpX0B0&result=1 (accessed May 25, 2019). 40_{Freund’s Latin Dictionary, 1951 ed. s.v. “Calx”}

41_{Ephraim Chambers, Cyclopædia, or, An universal dictionary of arts and sciences, (London, 1728), 141.} 42_{Chambers, Cyclopædia, 141.}

43_Ibid.

(21)

20

sense of deliberate obfuscation by the writers here; after all the alchemical recipe instructions to make lime are uncharacteristically straightforward, since we know what they are today. So, there is no reasonable argument that artists would be more esoteric in their recipe writing.

Now we will consider another source of information about alchemical calcination to further understand this process: alchemical illustrations.

Illustrations

Calcination is one of the key alchemical processes, and was illustrated in printed books both

mystically (Figure 4) and in not so obscure ways (Figure 5). Furthermore, investigation of illustrations of workshop techniques in printed books or manuscripts is an important art technological source for today’s researchers, as in earlier times there were no cameras to document workshop practice. However, as will be shown, the use of illustrations may be limited in reconstructing a technology, as artistic license will affect what is depicted.

If any doubt exists about interpretation of the image in Figure 5 for the process of calcination, “calcinatio” inscribed on the table in this image puts it to rest. Interpretation of the characters in Figure 5, such as the apparent sun king and queen or the lion and snake, is out of the scope of this thesis. What this image does offer, however, is a view of a kiln (for calcining materials) in operation. At the base is a door to ventilate and tend to the furnace. On the second tier is a smaller door apparently for the substances to be added to the kiln, using the tongs held by the alchemist. It seems likely that this is an alchemical kiln specifically for calcination or metalworking, as the small door is inadequate for pottery or bricks to be placed in the kiln in large batches.

However, we will now see how there can be problems with this simplistic interpretation. The image in Figure 5 is part of a series and reproduced from J. D Mylius’ 1622 publication Pilosophia Reformata in

(22)

21

a modern book. That book’s author, Stanislas Klossowski de Rola, without reference, says they “constitute one of the finest collections of alchemical engravings in existence.”45_{He goes on to}

describe how “many of them have been used by other alchemists to illustrate their own texts.”46

However, the story does not start in 1622. In 1618, Michael Maier published the Tripus Areus, an illustrated book on alchemy. This book is in fact a compilation that includes the Twelve Keys of Basil Valentine, an earlier alchemical text of notoriety, which may be the first published description of antimony.47_{However, to this thesis the part that matters are the depictions in the illustrations. The}

text describing twelve keys are twelve esoteric descriptions of laboratory practice. Each of the twelve keys was illustrated with its own engraving. The engraving of the twelfth key bears a striking

resemblance to Figure 5 (Figure 6).48

All of the symbols from that illustration, like the sun and moon and lion and snake are present here, but the furnace is quite different. Instead of the proper furnace of stone with two doors from Figure 2, this furnace appears as a metal or ceramic barrel with a small round door in the bottom, and smoke and flames escaping out the top. Another edition of Tripus Areus published in Germany in 1677 contains yet another set of illustrations (Figure 7).

This 1677 version also has the furnace as a barrel. Every other detail, including the two flowers and the lion devouring the snake are nearly identical across the three prints. This demonstrates that there were different ways to depict a furnace, in illustrating alchemical workshops, even though devouring animals and other symbols were codified in that time. Upon reflection it would seem that the rectangular two-tier kiln of the Mylius illustration, is the more realistic of the two possibilities.

45_{Stanislas Klossowski de Rola, Alchemy (New York, Avon Books, 1973) 98.} 46_Ibid

47_{C. S. Pierce, “Note on the Age of Basil Valentine” Science, 8, No. 189 (1898), 169-176.}

48_{This is the 1678 edition. It is clear that this engraving first appeared in the 1618 edition, but those editions are} in an unacceptable quality of digitization, or not copyright cleared for reproduction in this thesis.

(23)

22

Indeed, that two-tier kiln illustration is in fact in the general form of an athanor, the name for an alchemical furnace (Figure 8). The woodcut in Figure 8 comes from the book Alchemiae Gebri (1545). This kiln is round, and made of bricks with the doors on each tier as before. It is interesting that it shows some kind of shelf with round notches in it at the base of the second tier.

These are likely to hold crucibles, but may also be to collect ashes. The idea of the ash collection comes from the inexplicable fact the fire is clearly on the top, not at the base like a traditional fireplace. Are the two levels of doors present only for ventilation, and not to tend the fire? It is worth remembering that in this case the furnace looks like it is serving to heat substances within the bottle shaped container at the center, in a water bath. The illustrations are similar enough that it is quite possible that Mylius’ illustrator was simply copying the earlier furnace illustration, combining it with the symbolism from the Tripus Areus prints rather than observing a real furnace.

Stefan Michelspacher's Cabala: Spiegel der Kunst und Natur, in Alchymia (1615) is another illustrated alchemical book to discuss. This book has been written about from the viewpoint of addressing the illustrations for religious symbolism. Scholars argue that either these illustrations “loosely relate to depicting alchemical practice” or that they are a practical guide to alchemy.49_{However, there is no}

doubt that they are a depiction of early 17th_{century alchemy in some regard. Now let us look at the}

engraving. The first engraving in this book is described as illustrating calcination and entitled, in translation, “the mirror of art and nature” (Figure 9). This engraving is divided into three panels, of which only the bottom depicts laboratory work.

49_{Alinda van Ackooy. “Through the Alchemical Looking Glass: An Interpretation of Stephan Michelspacher’s} Cabala: Spiegel der Kunst und Natur, in Alchymia concerning the Tincture of the Alchemists” Master’s Thesis, University of Amsterdam, 2016. 8.

(24)

23

It has been described that this image is describing how both a wet and dry path towards calcination can be taken, the wet path clearly representing what we call distillation. However, for the remainder of the discussion, we will examine only details of the dry path calcination detail as shown in the bottom panel (Figure 10).

This image shows an alchemist working at a furnace. In his hand he holds a device called a diopter.50

This enables him to look inside the furnace without damaging his eyes, similar to modern welding safety devices. On the ground around him are various crucibles, tongs and fire caring tools. In the center is a quenching bucket of some kind, boiling away from the red-hot crucible placed in it. Beside the furnace are what would apparently be the most important tools to tend the furnace, a poker, tongs, and a bellows. The bellows are important to keep the furnace at the hottest possible temperature. On the wall directly behind the furnace are what appear to be small shovels. Below them is an indeterminate pile of material that could be ashes or fuel.

The possibility of the fuel being charcoal or coal is increased by the fact there is no stack of logs or chopped wood anywhere in this laboratory. By the distillation area on the ground are two baskets and tools including shovels (Figure 11). This larger basket being more likely the fuel storage, with the ashes swept away in the pile behind the furnace. The suggestion that this object is the coal basket is also found in the literature interpretation of this print.51_{Either way this is an important observation}

50_{van Ackooy, “Through the Alchemical”, 36.} 51_{Ibid, 35.}

(25)

24

since it indicates a possibility that firewood was not burnt in these furnaces. Burning better fuels than wood in these furnaces would have increased the temperature.

The furnace itself is very typical, if one interprets the image carefully. On the floor is a stone plinth, which has a sturdy table propped up on it. This should not be interpreted as a separate hearth. When one compares the actual two-tiered furnace set-up on the table to Figure 5, there is a resemblance, although the door on the upper tier is in a different position (Figure 12). Again, a pile of hot embers seems to rest on the very top of the furnace. However, these may be somewhat artistic licenses since a plume of smoke, sparks and flames flowing from a furnace is difficult to illustrate in black and white at this fine detail. In summary the Spiegel der Kunst und Natur, in Alchymia is an excellent source to investigate calcination technology in the early modern era.

To place these illustrations within the broader research question, as described above; there seems to be some confusion about applying this technique to ‘burning eggshells’ in recipes. As calcination of calcium carbonate is unsuccessful below 900 °C, it is no wonder that the alchemists worked on kiln technology, accessories such as the diopter and bellows, and use of different fuels in order to facilitate this reaction. If more research is to be done on alchemical furnaces in the production of artist’s pigments, reconstructions of those processes would be valuable. In this case, it is important to look closely at what is depicted in illustrations so we can build an historically accurate furnace to work with. The furnaces depicted in the illustrations are specific enough that not everything depicted was fantasy.

(26)

25

However, a question that remains from observing these illustrations is: when book illuminators wanted to make lime blue from a recipe, did those monasteries have access to calcination kilns to prepare burnt eggshells at 900 °C? Or, as described in the Pigment Compendium reference was ‘calx de testis ovorum’ sold at pharmacies ready-made? The alchemical instructions are usually clear as to what is being done, (calcination), but the artistic recipes not as much, simply calling it burning. In conclusion, when carefully interpreted, these images above describe what was necessary in

alchemical laboratories in the early modern period to process eggshells for artist’s recipes. This helps us better understand the way eggshells were handled from kitchen to pigment grinding stone.

Modern Scientific View

From what has been discussed so far in this chapter, it is clear that the alchemists had highly developed calcination technology as a process, although they did not understand the chemistry behind it, as we do today. What follows is a critical assessment of the role calcination played in the alchemical and thus artistic recipe, from the viewpoint of scientific history.

In alchemical history in Europe, Jabir Ibn Hayyan (c. 721-815) is a crucial early figure, and considered a founding father of chemistry, who is believed to be from today’s northeast Iran.52_{He is part of the}

larger Arabic alchemical world, which while not inventing alchemy itself, allowed Greek alchemy to be brought to Europe during the Middle Ages. It is worth remembering that his biographical details were “convoluted” as early as the 10th_century.53_{In the West, he has become known as Jabir, or Gerber}

when Latinized. The true meaning of his corpus, and how it came to the West, is still debated by historians. In one particular recipe, Jabir instructs the reader to take the “best quality of white calx of eggshell” as a recipe ingredient. 54_{This bears closer examination. Would not eggshell lime always be}

white?

Certainly, it is prescient, as referenced above, that Cennino Cennini desired calcined bone to be whiter than ashes. However, what can be said specifically about eggshell lime? The alchemists of Europe were aware of this property. Paracelsus (1493-1541) discusses in his book, Aurora

Thesaurusque Philosophorum, hens-eggs and eggshell lime as ingredients. Henceforth, this book will be referred to as simply Paracelsus’ Aurora. The version of that text used here is the publication which was “faithfully Englished (sic)” in 1659 by J. Oxon. In it we read a description of eggshell calx “as white as snow” in a recipe for the fixation (transmutation) of mercury. 55_{In conclusion the white}

nature of an eggshell lime as an indicator of quality is well documented in the alchemical literature. It could be inferred that this purity concept was known as early as the 8th _century.

The white qualification of eggshell lime described by Jabir, continues to be a noted property in eggshell lime production history. The instructions given in the book The Art of Chymistry (sic) (1668) by P. Thaibault, are also worth mentioning. The details of the process and ingredients of this recipe will be discussed elsewhere in this thesis. For the present, what matters is the descriptor that the calx

52_{Amr, Samir S. and Tbakhi, Abdelghani. “Jabir ibn Hayyan” Annals of Saudi Medicine, 27 (1), (2007) 52-3.} 53_{Thomas F. Glick, Steven John Livesey, Faith Wallis, Medieval Science, Technology, and Medicine: An}

Encyclopedia, (London, Taylor and Francis) 2005, 279.

54_{A. Y. Al-Hassan Science and Technology in Islam: Technology and applied sciences (New York, UNESCO, 2001)} 58-59

(27)

26

of eggshells produced is as “white as snow.”56_{So, more than a hundred years after the death of}

Paracelsus, this is still an important aspect to lime production from eggshells. Naturally, this may simply be an uncredited quotation of Paracelsus’ writing by Thaibault.

This visual property of the lime has been recorded in other sources, from our own time. An

interesting connection to modern research can be found in a journal article describing eggshell lime’s use in making ‘green’ mortars for historic building restoration.57_{This article regrettably makes no}

reference to the history of eggshell lime in cultural heritage, or even lime history in general. The purpose of this reference is to show ESL (eggshell lime) alongside CL (commercial lime, from

limestone) (Figure 12). For comparative purposes to other research, the illustrated eggshell lime was calcined at 1000 °C. Another illustration in th3 article shows the author’s steps to produce slaked lime from the raw shell (Figure 13).

Here is a good place to address the main research question of this thesis; why not use chalk instead of eggshell to make lime? As was shown in Chapter 1, calcium carbonate comes from many different sources such as travertine, chalk, and limestone. Lime for mortar has been made since antiquity from many different sources of calcium carbonate. Seashells have been used to this end, and are just more practical to use for industrial scale production verses chicken eggshells. Also, as lime is a

mass-produced product for construction projects the chances that impurities would affect the final product is high. There is one reference, again from our own time that tentatively addresses this. Lime mortar prepared from Lincolnshire chalk is sold online for building restoration. This is indeed part of the same chalk deposit described in Figure 1. The product is described as cream coloured.58_{So perhaps}

even natural chalk does not produce a lime as ‘snow white’ as eggshells do, because of mineral

56_{P. Thaibault, The Art of Chymistry: As it is Now Practiced, (London, John Starkey, 1668). 208}

57_{Kevin Beck et. al. “On the use of eggshell lime and tuffeau powder to formulate an appropriate mortar for} restoration purposes” Geological Society London, Special Publication. 331, (2010) 137-145.

58_{Mortar Grade Chalk Lime Putty; Rose of Jericho, n.d.} https://www.roseofjericho.co.uk/product/mortar-grade-chalk-lime-putty Accessed June 3, 2019.

(28)

27

impurities. Another important point for research and reconstruction is in Figure 13; apparently it does not matter if the shells used in calcination are from brown eggs. This means that any hen’s eggshells could be used to make lime that was very pure. Again, it seems that tacit knowledge is something in the recipes where no one acknowledges the exact kind of (chicken) eggshells that are burnt.

However, once you have learned more about the process, you understand that it actually doesn’t matter.

In the spirit of the alchemists described above, today’s entrepreneurs are seeking high quality lime for industrial applications. To that end, many peer reviewed articles about the process of calcining eggshell appear in chemical engineering or agricultural journals. So it was valuable to consult those sources to get a modern perspective on this alchemical ingredient. It is worthwhile pointing out, as mentioned further in Chapter 4, that nearly all of the modern scientific studies of eggshell lime were conducted at southeast Asian and Indian universities.59_{Therefore, there is potential for a difference}

between the exact physical properties of those eggs and historic eggs in Europe, where the artistic recipe usage flourished. Scientific proof that these differences could affect the lime prepared from it, is addressed in Chapter 4. One of these Asian research articles describes the colour properties of restaurant waste eggshells (in Indonesia) as they are heated in a modern furnace with measured temperature gradients.60_{Their results are illustrated below (Figure 14). Only at 900 °C and above is}

the product made stark white again, which is shown in the analysis to be almost pure calcium oxide. In other words, by examining the modern replication of the original eggshell lime, it is suggested that a bright white appearance is a sign that high temperature calcination results in high chemical purity.

59_{This is likely due to the fact that hot, humid climates would naturally invest more in the hygienic recycling of} food waste.

60_{Risfidian Mohadi et al. “Preparation Calcium Oxide (CaO) from Eggshells” Sriwijaya Journal of the}