Category Archives: Dupre Project

True Colors, or the Revelatory Nature of Cold

By Thijs Hagendijk

Heat is transformative, brings about change, separates substances or bring them together. Every student of chemistry knows how to enable or enhance a chemical reaction by applying energy to a system, usually in the form of heat. Early modern practitioners did not think otherwise. Fire was the transformative element and key to the production of all kinds of different materials, ranging from the philosopher’s stone to artisanal products such as glass, porcelain or pigments. Applying heat to bring about change is publicly ingrained thermodynamics, but one thing is even more obvious. Once heated, things have to cool down again.

Figure 1: Eikelenberg’s notes on the art of painting, comprising five different manuscripts. Photograph: Regionaal Archief Alkmaar.

When the request came to write a blogpost on cold and recipes, I was somewhat hesitant. Heat seems to elicit the most interesting stories and anecdotes, but interesting cases with respect to cold failed to come to mind immediately. Hence, I tried a different approach and looked at how cold featured in a collection of overtly practical notes on the preparation of paint materials collected by the Dutch polymath and painter Simon Eikelenberg (1663-1738). Intended for publication, he promised his readers an “accurate descriptions of the origin of making, preparation and general use of paint materials, oils, mix-fluids and varnishes.”[1]  It was within the confines of this manuscript that I began to discern two themes with respect to cold in practices of making.

Figure 2: Reconstruction of one of Eikelenberg’s varnish recipes. The varnish was prepared in a glazed pot, placed in a sand bath and heated on fire. Photograph: Thijs Hagendijk.

It is only when things have cooled down that the transformative work of heat can really be judged. Eikelenberg describes for instance how he experimented with minium, a red lead-based pigment, which he heated in a crucible and placed in a fire. “The more it glowed, the more the minium turned yellow near the sides of the crucible, the lowest parts alike; which, when it was cold, appeared to be nothing else but yellow massicot.” [2] Eikelenberg also describes the preparation of various varnishes. Here too, quality and properties of substances are explicitly observed after the varnishes have cooled down. “When the varnish was cold I found that it was rather thin and that it did not cover well.” [3]  Another varnish was prepared on a hot sand bath, after which Eikelenberg “filtered it through a cloth and let it cool: it appeared then as a thickish and yellowish varnish.” [4]  Pay attention to the word “then”: there is a clear order of things that speaks through Eikelenberg’s notes. Being cold is a condition that precedes testing and Eikelenberg makes that rather explicit.

Figure 3: It is hard to achieve a homogeneous mixture when preparing varnishes. A whitish sediment is developing in this varnish, which is in coherence with Eikelenberg’s notes. Photograph: Thijs Hagendijk.

Whereas heat is transformative, it is only in the absence of heat that things can be trusted to stay the same. Continuing with the varnishes, Eikelenberg was well aware that their preparation does not stop after the ingredients have been heated and combined. As long as it is still hot, the apparently homogeneous concoction can easily coagulate and fall apart. Eikelenberg wrote in his notes: “We can conclude that to prevent curdling it is necessary not to stop stirring before the mixture is cold.” [5] Indeed, each time he made varnishes, Eikelenberg made sure to keep stirring until everything was cooled down: “stirring steadily until all was cold” or “having stirred until it became cold”.[6]

Figure 4: Eikelenberg mentions that: “[w]e can conclude that to prevent curdling it is necessary not to stop stirring before the mixture is cold.” Passage marked in red. Photograph: Regionaal Archief Alkmaar.

For Eikelenberg, heat was both friend and foe and until his varnishes reached firm, cool ground, they required careful guidance and attention. Cooling down was thus as arduous a process as heating the mixture was in the first place. Yet, once cooled down, true colors are revealed – deprived from heat and stabilized by the cold.

[1] Simon Eikelenberg, “Aantekeningen betreffende schilderen,” MS 391, Collectie Aanwinsten, Regionaal Archief Alkmaar: fol. 1. “Naukeurige beschrijving van de oorsprong of making, bereiding en ’t algemeen gebruik der verfstoffen, olijen, mengvogten en vernissen.”
[2] Simon Eikelenberg, “Aantekeningen betreffende schilderen,” MS 390, Collectie Aanwinsten, Regionaal Archief Alkmaar, fol. 806. Original: “na mate dat het gloejend wierd, veranderde de menij die naast tegen de zijden van de kroes aan-zat en wierd geel, gelyk ook ’t onderdtste; ‘t welk doe ‘t kout was niet anders dan gele masticot geleek”.
[3] Eikelenberg, “Aantekeningen betreffende schilderen,” MS 390, fol. 827. Original: “Doe de vernis koud was bevond ik ze wat dun en datze niet genoeg dekte.” Translation from: A. van Schendel, “Simon Eikelenberg’s Experiments on the Preparation of Varnishes,” Studies in Conservation 3 (1958), 130.
[4] Eikelenberg, “Aantekeningen betreffende schilderen,” MS 390, fol. 802. Original: “Doe ‘t wel vermengt was, kleijnsde ik ‘t door een doek en liet het kout worden, wanneer ‘tzelve een dikagtige en geelagtige vernis vertoonde” Translation from: Schendel, “Simon Eikelenberg’s Experiments,” 128.
[5] Eikelenberg, “Aantekeningen betreffende schilderen,” MS 390, fol. 824. Original: “Hieruijt kan men afnemen dat om ’t schiften voor te komen, men niet moet op-houden met roeren voordat se kout is.” Translation from: Schendel, “Simon Eikelenberg’s Experiments,” 129.
[6] Eikelenberg, “Aantekeningen betreffende schilderen,” MS 390, fol. 827. Original: “gestadig omroerende totdat het gantschelijk koud was.” Translation from: Schendel, “Simon Eikelenberg’s Experiments,” 130. Eikelenberg, “Aantekeningen betreffende schilderen,” MS 390, fol. 832. Original: “tot koutwordens toe geroert te hebben”.

 

A forgotten chapter in natural history: the taxidermy of man

By Marieke Hendriksen

Having written a book on eighteenth-century anatomical collections, I know a thing or two about historical techniques for preserving (parts of) the human body. As I am interested in natural history collections more generally, I also did some research on the preservation of animal bodies, and even took a taxidermy course myself. However, recently I realised that the preservation of human and animal bodies were historically even closer connected than I had imagined. Yet ideas about which parts of the human body could and should be preserved, and how, diverged greatly, particularly when it comes to skin, or taxidermy. Taxidermy, from the Greek τάξις (taxis) and  δέρμα (derma – I am adding those for people who may not read Greek script), literally means ‘the arranging of skin’.

Fragment of an engraving of the anatomical theatre of Leiden University, early 17th century, showing visitors who appear to discuss a human skin. Contemporary engraving by Willem Swanenburgh; drawing by Jan van ‘t Woudt (Johannes Woudanus).

There are a few known cases of attempts to preserve human skins in their entirety before 1800 – for example, there was a human skin in the Leiden anatomical theatre in the seventeenth century – but that wasn’t stuffed, and such attempts appear to have been altogether unsuccessful. If human skin was preserved, it was mostly small pieces, which were used to study things like skin colour and structure, tattoos, or pathologies. By the end of the eighteenth century, the preservation of an entire human skin in a lifelike pose was of little interest to anatomists. Normal internal anatomy would be studied through dissection and the creation of preparations and skeletons, and pathologies of the skin could be preserved by making preparations of small sections of skin. As healthy skin can be studied perfectly easily in live subjects, there was little reason to pursue the taxidermy of man. This is reflected in anatomical handbooks like Thomas Pole’s 1790 Anatomical Instructor (reprinted in 1813), which gave detailed directions for numerous methods to preserve parts of the human and animal body, including entire heads and foetuses, but did not say anything about how to preserve only skin. On the contrary, Pole advised to remove the cuticle from a head that was to be preserved,  as this would give ‘a brightness to the complexion’.[1]

Jeremy Bentham’s ‘preserved’ head is not on display, but stored in an environmentally controlled safe. Copyright: UCL.

However, with the growing popularity of taxidermy – the mounting of animal skins in lifelike poses – and the rise of physical anthropology in the early nineteenth century, there were a number of experiments with human taxidermy, the most famous of which was probably Jeremy Bentham’s unsuccessful attempt to have his body made into an ‘auto-icon’ after this death. Then there was ‘el negro’ or ‘the negro of Banyoles’, whose faith was described by Dutch author Frank Westerman in his 2004 book El Negro en ik (‘El negro and I’). The remains of this young African San man were stuffed by two taxidermists, the French Verreaux brothers, in the 1830s, and remained on display in a local Museum in Banyoles, Spain, until 1997. Eventually his remains were send for burial in Botswana in 2000. Jules Pierre (1807-1837) and Jean Baptiste Édouard (1810-1868) Verreaux created taxidermy specimens of exotic animals for their father’s Parisian shop in natural historical objects, Maison Verreaux, and, as ‘el negro’ shows, used human bones for his models.

The head of the figure in ‘Arab Courier attacked by lions’ sits detached from the rest of the diorama during restoration work. Copyright: Nate Smallwood | Tribune – Review

For a long time, ‘el negro’ was the only known case of nineteenth-century human taxidermy. However, a recent discovery suggests that the Verreaux brothers used human remains more frequently. In 2016, a human skull was discovered in a mannequin that was part of an ensemble made by the Verreaux studio. Formerly known as “Arab Courier Attacked by Lions”, it was restored and returned to display at the Carnegie Museum of Natural History in Pittsburgh under the title “Lion Attacking a Dromedary”. Although apparently no attempt was made to use human skin in the Pittsburgh diorama, these cases show that there was little reticence when it came to using human materials for taxidermy displays in the nineteenth century, particularly when the human in question was considered ‘exotic’. This is supported by the fact that a popular contemporary taxidermy manual, aimed specifically at museums and travelers, opened with a paragraph on the impossibility of applying taxidermy to man successfully. The book, written by the naturalist Sarah Bowdich (née Wallis, later Lee, 1791-1856) saw six editions – the first in 1820, the last in 1843.

After listing the necessary tools and giving a number of recipes for the cleansing and preservation fluids used in taxidermy, Bowdich opened the section on ‘the preparation of mammalia’ with a somewhat disappointed-sounding statement:

1. Of man 

All the efforts of man to restore the skin of his fellow creature to its natural form and beauty, have hitherto been fruitless: the trials which have been made have only produced mis-shapen, hideous objects, and so unlike nature, that they have never found a place in our collections.

Bowdich went on to discuss the life-like wet preparations made by Amsterdam anatomist Frederik Ruysch (1638  – 1731) as ‘without doubt (…) very useful to science’, before switching to a description of a more successful practice – the preservation of skeletons. Given the tragic history of ‘el negro’ and many other violently obtained human remains in museum collections, it is a cold comfort that the naturalists of the nineteenth century failed at the taxidermy of their ‘fellow creature’.

[1] Pole, Thomas. The Anatomical Instructor ; or an Illustration of the Modern and Most Approved Methods of Preparing and Preserving the Different Parts of the Human Body and of Quadrupeds by Injection, Corrosion, Maceration, Distention, Articulation, Modelling, &C. London: Couchman & Fry, 1790: p.84.

What’s in a name: Plaster of Paris

By Marieke Hendriksen

One of the problems we face as historians studying and reconstructing recipes is that the names describing ingredients, tools, and materials change over time, and that the meaning of terms itself changes over time. This is even the case with relatively recent recipes and materials that are in theory unchanged as I recently discovered. As part of my research for the ARTECHNE project, I recently looked at instructions for making anatomical casts from plaster from 1791.

Painted plaster cast of a large fibroma of the jaw, 1830s. Courtesy Surgeons' Hall Museums, RCSEd.
Painted plaster cast of a large fibroma of the jaw, 1830s. Courtesy Surgeons’ Hall Museums, RCSEd.

The creation of anatomical casts and models using plaster of Paris became increasingly popular towards the end of the eighteenth century, fuelled by the omnipresence of plaster in the visual arts and interior decoration, and the increasing importance of pathology and later physiognomy within the study of medicine. The latter meant that medical men were looking for durable three-dimensional ways to preserve diseased bodies and body parts that could not be preserved otherwise (e.g. in a preparation), either because decay could not be stopped or because the patient was still alive.

Johan Zoffany, The Portraits of the Academicians of the Royal Academy, 1771-72
Johan Zoffany, The Portraits of the Academicians of
the Royal Academy, 1771-72. Note the plaster models of antique statues around the room.

In his 1790 book The Anatomical Instructor, physician Thomas Pole (1753-1829) not only gave advice on how to make anatomical preparations and drawing, but also included over fifty pages on how to create, colour, repair and maintain plaster casts and models. Pole started the chapter on modelling with outlining the relevance of the quality of the plaster of Paris, or calcined alabaster, that was to be used. He explained that

Illustration of how to make a cast of a diseased bone from Pole's 1790 'Anatomical Instructor'
Illustration of how to make a mould of a diseased bone from Pole’s 1790 ‘Anatomical Instructor’

“…that of a middling price is used for making of moulds; the finer sort is for casts, to be poured first into the mould, when properly prepared; after it has formed a layer of about half an inch, more or less, according to circumstances, then the coarser sort is to be used to fill up the mould, or to give it sufficient thickness.”[1]

But exactly what were the various qualities of plaster for sale in London in the 1790s made of? The term ‘calcined alabaster’ tells us little, as alabaster was and is a collective noun that designates both various kinds of light-coloured, translucent and soft stone used mainly for carving decorative artefacts (often the minerals gypsum or calcite – the former much softer than the latter), and a specific compact and fine-grained variety of gypsum. In the decades after Pole’s publication, the French chemist Antoine François de Fourcroy (1755 –1809) would distinguish nine kinds of calcareous sulfate, one of which was sulfate of lime or common gypsum. In an 1810 ‘dictionary of the arts’ Fourcroy’s sulfate of lime or common gypsum was described as follows:

“Sulphat of lime, or common gypsum, or plaster-stone. This substance is white, more or less inclining to grey, interspersed with small brilliant crystals, easily cut with a knife. it is found disposed in Paris. We shall hereafter find, that it is not pure selenite, but owes its most valuable property, as plaster, to the admixture of another kind of earth. (…) Calcareous sulphat is likewise found dissolved in waters, as in the well-waters of Paris; it is never pure, but always combined with some other earthy salt, with base lime or magnesia. This salt has no apparent degree of taste. It decrepitates if a sudden heat be applied to it; it is then of an opaque white, in which state it is called fine plaster, or plaster of Paris: by this calcination it loses about twenty in one hundred.”[2]

Entrance to the Montmartre gypsum quarry. Probably early 19th century, artist unknown.
Entrance to the Montmartre gypsum quarry. Probably early 19th century, artist unknown.

As this fragment suggests, plaster of Paris indeed derives its name from a large and very pure gypsum deposit at the Montmartre and Menilmontant hills in Paris – there were plaster quarries at this site at least as early as the year 500. This led “calcined gypsum” (roasted gypsum or gypsum plaster) to be commonly known as “plaster of Paris”, even after the exhausted quarries were converted into Montmartre cemetery and the Buttes de Chaumot gardens respectively in the mid-nineteenth century. Although not all plaster came from Paris at the time Pole was writing, there is a fair chance that much high-quality plaster was indeed plaster from Paris.

Today, gypsum plaster, or plaster of Paris, no longer comes from Paris, but is still produced by heating powdered gypsum to about 150 °C. When mixed with water, this forms a paste that will harden within minutes, producing an exothermic reaction, which means it warms up. You can easily buy ‘plaster of Paris’ from artist’s supplies shops and online retailers, but none of these mention the exact chemical composition. Yet before I (or anyone else) can try my hand at reconstructing Pole’s instructions I will need to find out whether the best, finest plaster of Paris still contains a percentage of lime or magnesia, what the ‘coarser varieties’ that Pole described contained, and whether these are still available.

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 648718), and was supported by the Wellcome Trust (grant number 203403/Z/16/Z).

[1] Pole, Thomas. The Anatomical Instructor ; or an Illustration of the Modern and Most Approved Methods of Preparing and Preserving the Different Parts of the Human Body and of Quadrupeds by Injection, Corrosion, Maceration, Distention, Articulation, Modelling, &C. London: Couchman & Fry, 1790: p. 202-3.

[2] Wilkes, John. Encyclopaedia Londinensis, Or, Universal Dictionary of Arts. Vol. 4. London: J. Adlard, 1810: p. 230.

 

Topazes, Emeralds, and Crystal Rubies. The Faking and Making of Precious Stones

Marjolijn Bol

Today the making and illegal selling of factitious stones has reached an unseen level of sophistication. Advanced technologies allow man to produce synthetic versions of the most precious of stones – diamonds, emeralds, sapphires and rubies (fig. 1). So convincing are these synthetic gems they can only be distinguished from natural precious stones in laboratories with advanced spectroscopic devices.

Fig. 1 Synthetic gemstones
Fig. 1 Synthetic gemstones

The making of imitations of precious stones is not just typical of our modern age. In fact it dates back to at least Egyptian times, as graves from this period show that glass was used to substitute for jewels. Seneca (AD 1 – AD 65) and Pliny the Elder (AD 23- AD 79) were the first authors to write about the practice. Whereas Seneca only mentions that ‘sometimes stones are boiled to resemble emerald (smaragdus)’, Pliny provides us with a rather lengthy account in which he explains the various ways in which gems were imitated. He mentions that glass pastes were used for the imitation of seals and that in some cases stones were cemented together to imitate sardonyx. By a third method, ‘Indian crystals’ were colored with certain dyes to make them look like more expensive minerals. These ‘gems’ were apparently so convincing that ‘(…) there is considerable difficulty in distinguishing genuine stones from false; the more so, as there has been discovered a method of transforming genuine stones of one kind into false stones of another.’ While some physical evidence still survives of the first two practices, the factitious gems made by the third manner, has barely, if at all, come down to us. The many recipes that explain how to make such imitation stones (surviving from the fourth well into the sixteenth century) nevertheless suggest that this last method must have also been practiced, and perhaps even on a large scale. I therefore hoped that a physical reconstruction of the imitation gems might give some further insight into the appearance of these imitation gems. Would it be possible, as the recipes suggest, to make a convincing imitation of a precious stone? Could such a ‘fake’ potentially fool the innocent eye into thinking it was real?

The earliest examples of recipes for imitating stones can be found in the so-called Stockholm Papyrus, a recipe collection written in Greek at about 200-300 AD. The Papyrus includes no less than 71 how-to’s for the imitation of precious stones with lesser materials, including ruby, beryl, amethyst, sunstone and emerald. In subsequent centuries, numerous other recipe books include similar instructions for making counterfeit stones. While the recipes are various, they are almost all based upon two basic operations that I have attempted to reconstruct (fig. 2).

Fig. 2 Opening up of stones
Fig. 2 The opening up of stones

First, a transparent mineral, such as rock crystal, selenite, or topaz, is roughened or ‘opened up’. Following the recipes instructions, I investigated this by cooking the minerals in potash alum (potassium aluminium sulphate) dissolved in vinegar. As soon as I removed the heat from this mixture, it rapidly crystalized into a hard crust around the stones. In accordance with the recipes I left the stones overnight.  Nevertheless, when I inspected them the next day (after having chiseled them out) I could not see any changes. Regardless of whether the stones were successfully ‘opened up’, the coloring of the minerals did produce some surprising results.

The recipes instruct that the ‘opened up’ mineral should be colored using a mixture of a colorant ground with oil or resin to make it assume the appearance of a specific gemstone. The dyes and pigments used varied according to the type of gemstone that was to be imitated. A red dye made from alkanet root (used by ancient cloth dyers) was advised for the imitation of rubies and the green copper pigment verdigris was used to transform transparent minerals into emeralds. For my first reconstructions I choose to make a ‘fake’ emerald. It was one of the precious stones imitated the most frequently and the instructions for making it remained almost the same through (post-) classical and pre-modern times (fig. 3).

Fig. 3 Coloring of stones
Fig. 3 The coloring of stones

I first ground the pigment verdigris with linseed oil and used this substance to cover the base of a rock crystal, topaz and piece of selenite. This resulted in a beautiful, translucent green stone that, due to the instability of the pigment verdigris, in time assumed the saturated forest green color of a real emerald. Whereas more reconstructions are certainly required to investigate the nature of this method of gemstone imitation, these first experiments show that, when ancient sources insist how visually convincing the imitations of precious stones could be, they are probably not exaggerating.

Fig. 4 Emerald imitation
Fig. 4 Emerald imitation

Recommended reading:

Marjolijn Bol, ‘Coloring Topazes, Crystals and Moonstones: The making and meaning of factitious gems, 300-1500’, in Marco Beretta and Maria Conforti (eds.), F for Fakes: Hoaxes, Counterfeits and Deception in Early Modern Science, 2nd Watson Seminar in the History of Material and Visual Science, Museo Galileo, Florence, June 7, 2013, Science History Publications (Brill Publishers: 2014), pp. 108-129.

Earle R. Caley, “The Stockholm Papyrus: An English Translation with Brief Notes”, Journal of Chemical Education 4 (1927), pp. 979-1002.

Pliny, The Natural History, books 33-37 (book 36 includes Pliny’s natural history of stones): http://www.perseus.tufts.edu/hopper/text?doc=Plin.+Nat.+toc