How to correct Plato, alchemically?

By Bojidar Dimitrov, AlchemEast Project

Jabir Ibn Hayyan is a figure of key importance for the development of alchemy and chemistry. A vast body of literature virtually covering the entire spectrum of ancient science has been attributed to the Islamic polymath, and yet much of the little we know about him remains shrouded in mystery. The very historicity of Jabir’s person and the authenticity of his works have been the subject of rigorous scholarly debate. This is largely due to the fact that the majority of the texts which belong to the Jabirian corpus have not been edited and published.

The scant biographical data provided by mediaeval Islamic sources and Jabir’s own works suggests that his lifetime spanned the period between ca. 721/725 and 812/815 AD. The so-called Jabir Problem mainly revolves around different aspects of this alleged historical context. The ambiguous relationship between the Arabic Jabirian corpus and the nascent alchemical tradition of the Latin West is the other major side of the conundrum. 

Paul Kraus’ ground-breaking studies on Jabir[1] proposed that the Jabirian corpus was probably compiled over a longer period of time by a school of alchemists who circulated their works under Jabir’s name. Similar doubts were already expressed by mediaeval Islamic scholars, and Kraus’ detailed analysis of the language and the content of seminal texts argues that the scientific terminology, doctrines and references to Greek authorities found in them point to a later stage of Islamic intellectual history, which began in the ninth century. Kraus’ conclusions have been debated by scholars since their publication in the 1940s, but the scope and depth of his research remain unmatched to this day.

One of the current objectives of the AlchemEast Project is to make available a collection of alchemical recipes belonging to a sub-genre of Jabir’s corpus. Plato’s Rectifications is the only surviving collection of a cycle of pseudepigraphical ‘rectifications’ associated with ancient authorities. The work is presented as a commentary on alchemical doctrines ascribed to Plato that the Greek sage is said to reveal to his disciple, Timaeus. The ninety recipes involve alchemical procedures with mercury which are intended to illustrate the application of Plato’s theories.

Socrates discussing philosophy with his disciples (from a thirteenth-century Arabic manuscript).

Jabir’s attribution of alchemical material to Plato is pertinent to the reception of Platonic influences in Islamic alchemy and the wider context of Islamic thought. While Jabir’s system incorporates key Neoplatonic traits of Greek philosophical alchemy, its experimental and arithmological developments are highly original and do not seem to derive from extant Greek texts. Furthermore, no alchemical texts are attributed to Plato (or Socrates) in the Greek tradition.[2] There are, however, Syriac recipes attributed to Plato, and he is generally accorded a prominent place in Arabic occult literature. Such facts may indicate that Jabir could have been influenced by late antique Neoplatonic traditions of a distinctly Near Eastern flavour.

An excerpt from Rectification Nr. 14 presents a recipe which involves the heating and cooling of mercury:

Then he said: take ten measures of spirit (i.e. mercury), put it in the middle gourd (i.e. glass vessel), and tighten upon it the alembic which has no aperture (i.e. valve). Heat it over gentle fire for ten days, then cool it off on the eleventh. Repeat the operation and gather the first water. The gourd containing mercury will be heated, or joined to the other gourd until it (i.e. mercury) dissolves in one of the two gourds. Take the thickened [residue], put it in the second gourd, and heat it until it melts, becomes liquid and turns red. Then heat the water until it boils and [the condensate] starts dripping all over the residue, [so that] it swells, absorbs some of the water and is incerated by it, and yields. It will become like wax, just as we described initially, and [even] better. If the procedure starts by heating the water until [the condensate] drips over the residue, it will be dissolved, and both will be dissolved, coagulated and incerated together, [and thus the procedure] is also complete. Peace.

Image 2: Depiction of alchemical apparatus with an alembic (MS, BNF Arabe 6915)

Depiction of alchemical apparatus with an alembic (MS BNF Arabe 6915).

The text exemplifies the fluidity of content that alchemical recipes often exhibit. The procedures it describes are relatively simple, but the textual variants in the manuscripts allow different possibilities. The translation above is not conclusive, since the relationship of the alembic and the two vessels is somewhat ambiguous. According to certain readings, for instance, the second vessel and the alembic must be alternated during the process of dissolution. The examination of further textual variants and manuscripts can expand our understanding of Jabir’s technical methodology. Ultimately, the intertextuality of Platonic pseudepigrapha found in Jabir and other traditions calls for an overarching discussion of Plato’s role in alchemical discourse. Whether this role was itself rectified by practitioners over the centuries, or the fluctuations we encounter in manuscripts are of a purely textual nature, are the main questions AlchemEast aims to address.

[1] Paul Kraus, Jābir ibn Ḥayyān. Contribution à l’histoire des idées scientifiques dans l’Islam, Vol. II. Jābir et la science grecque (Cairo: Mémoires de l’Institut d’Égypte 45.1, 1942).

[2] Ibid., p. 58.

Boiling Milk: Experimenting with Boerhaave’s Little Furnace, Part III

By Ruben Verwaal and Marieke Hendriksen

Fig. 1. Ruben keeps an eye on the temperature.
Fig. 1. Ruben keeps an eye on the temperature.

It has been exactly 350 years since Herman Boerhaave’s birthday. What better way to honour the renowned professor than to redo some of his old experiments? 

On Monday 31st of December, in the year 1668, Herman was born. And already as a kid, he and his brother James probed the curiosities of nature: plants, minerals, liquids and bodily fluids. As Herman recalled some 30 years later, “how many whole days and nights we have spent successively together in the chemical examination of natural bodies” [1]. It must have been around this time that Herman invented his little furnace.

“I’ll put an alarm to take the milk out of the freezer,” Marieke texted Ruben the week before New Years’. Between all the Christmas dinners, the 31st was the only day still free to meet up over the holiday. Weeks before we had bought Irish turf online and collected raw milk from a farm near Delft, as well as from a breastfeeding friend . Having finally found the time, we gathered their materials together and started experimenting.

Why Milk?

As a physician, Boerhaave was fascinated with the human body. How does it work? What is it made of? Boerhaave soon realised that a newborn solely grows on breastmilk. Mothers eat their food and digest it with juices from their intestines; after circulating in their bodies, the fluid concocts into chyle and develops into the maternal sustenance in their breasts. Not only human babies, Boerhaave reasoned, but all mammals are nourished by milk and can grow solely on it. “Milk, therefore, appeared to be the first thing to be examined.” [2]

Making Curd

Fig. 2. 4PM: Raw milk heated with vinegar gives you cheese - well, sort of.
Fig. 2. 4PM: Raw milk heated with vinegar gives you cheese – well, sort of.

We set out to replicate the first experiment, titled “fresh cow’s milk coagulates with acids, even in a boiling heat.” We lit the turf in the fireplace. Once it was hot, glowing, and smelling, Marieke put some in an earthenware bowl and placed it in our wooden furnace to let it heat up. Meanwhile Ruben added vinegar to fresh milk in a glass vessel. As the fluid was gradually heating up in our furnace, parts of the mixture were slowly coagulating into curd.

We were basically imitating the cheese-making proces – a more than common practice in the early modern Dutch Republic. Boerhaave, however, assigned physiological significance to this process. For the cheese could be hardened and burned, smelling like bone – proving that even the hardest parts of a baby’s body could have its origin in milk. “This is a strange change of so fluid a matter as milk, but is, perhaps, the origin of all the solids in the body.” [3]

Red Milk

The second experiment was to show how “recent cow’s milk coagulates, turns yellow, and red, by boiling over the fire with fixed alcali.” We basically repeated the previous steps, but instead of using vinegar we added ammonia. Slowly but surely, the white fluid indeed turned yellow, then a dark orange – and was about to turn red. Here we had to stop, unfortunately, because the turf was cooling down, and it was getting dark outside.

Yet via this relatively simple process, Boerhaave confirmed a common illness: milk fever. The milk from mothers suffering from fever “becomes yellow, saline, thin and sanious.” [4] It also clarified why Dutch cows gave yellow milk during the 1714 outbreak of cow’s fever.

Fig. 3. 6PM: Raw breast milk heated with ammonia: 'bloody' milk?
Fig. 3. 6PM: Raw breast milk heated with ammonia: ‘bloody’ milk?

So What Have we Learned?

First, turf smells! We can only surmise that our early modern colleagues were simply oblivious to the smell due to its omnipresence. Second, our apparatus passed the test. Boerhaave’s little furnace successfully kept the heat inside at an evenly distributed yet high temperature (around 60℃). This is an important feat, especially when working with milk. Anyone who has ever boiled milk knows how easily it becomes a big mess when you don’t pay attention for just two seconds. Yet we were able to have 15-minute glühwein and oliebollen breaks without any problem. 

Third, our experiments have shown us how relatively easily some of Boerhaave’s experiments can be replicated – as opposed to some of his contemporaries who made secret potions or applied intricate and dangerous procedures with metals and minerals. Historical reproduction, reconstruction, and re-enactment are methodologically complex and potentially problematic because of the impossibility of repeating history and reliving the experiences of historical actors. Yet our experiments do enhance our understanding of the past; they make our historical understanding more holistic, less linear and text-based. [5] For example, these experiments help us to understand why Boerhaave was such a popular teacher; with the help of a small oven based on his design, students could learn by doing. 

Fourth, with more time and patience we could have gained better results. This is the case with everything, of course. Yet some of Boerhaave’s experiments with milk – for example the milk turning sour by digestion (i.e. at 37℃) – is described as taking twelve days! Lastly, replicating early modern experiments is fun. We won’t deny that working on your object of study outside the library is refreshing. The photos and videos of the process have a public appeal too. We hope you enjoyed it.



[1] ‘Dedication’ in Herman Boerhaave, Elements of Chemistry (London, 1735), A3r.

[2] Herman Boerhaave, A New Method of Chemistry (London, 1741), 2, 185.

[3] Ibid., 187–188.

[4] Ibid., 188–189.

[5] Pamela H. Smith and Tonny Beentjes, “Nature and Art: Making and Knowing: Reconstructing Sixteenth-Century Life-Casting Technniques,” Renaissance Quarterly 63 (2010): 128–79. Marieke M.A. Hendriksen, Elegant Anatomy. The Eighteenth-Century Leiden Anatomical Collections (Leiden & Boston: Brill, 2015), Chapter 1. Donna Bilak et al., “The Making and Knowing Project: Reflections, Methods, and New Directions,” West 86th 23, no. 1 (2016): 35–55. Hjalmar Fors, Lawrence M. Principe, and H. Otto Sibum, “From the Library to the Laboratory and Back Again : Experiment as a Tool for the History of Science,” Ambix 63, no. 2 (2016): 85–97.

Archaeology and early modern glassmaking recipes: The case of Oxford’s Old Ashmolean laboratory.

By Umberto Veronesi

Crystal blown bottle decorated with milk glass festoon (festoni di lattimo), c. 17th c., Venice.  Image courtesy of Wikimedia Commons.
Crystal blown bottle decorated with milk glass festoon (festoni di lattimo), c. 17th c., Venice. Image courtesy of Wikimedia Commons.

The product of human ingenuity, glass perfectly embodies the alchemical power to imitate nature by art and since the Bronze Age it has proved an incredibly hard substance to classify. Although glass only requires sand, salts and the action of fire, a quick look at any recipe collection will reveal that glassmakers have used a vast array of ingredients depending on what materials were available to them and on the physico-chemical characteristics desired. Colours and opacity were provided by the addition of the right metallic oxides, but even a perfectly colourless glass required specific reagents.[i]

Here, I am going to explore three 17th-century recipes for white enamels, what Venetians called lattimo. Enamels are glass pastes that could be coloured according to the need and then used as paint or to counterfeit gems. There are plenty of recipes out there, many are listed in Antonio Neri’ L’Arte Vetraria. However, in this post I am going to take my start from a different set of “primary” sources, namely the very crucibles used to manufacture white enamel at one of Europe’s leading chymical laboratories, the Old Ashmolean in Oxford. The residues found stuck to the walls of the vessels (Fig. 1) contain the chemical fingerprint of the ingredients used. The analysis of small cross-sections of such residues with a scanning electron microscope (SEM) are therefore a way to explore the recipes.

Figure 2. Crucible fragments analysed with glassmaking residues.
Figure 2. Crucible fragments analysed with glassmaking residues.

The chemical composition of the three residues shows both similarities and important differences. All of them have high levels of silica, corresponding to sand, the main component of glass. To melt silica a fondant is essential, and it needs to be added to the crucible. Here, two residues (B and C) bear the traces of a potassium-based fondant, probably saltpetre or even salt of tartar. Residue A has sodium oxide instead, which means that a different fondant was, pure soda most likely. Recipe-wise, this is the first relevant difference. Next, a reagent must also be added in order to render the glass paste white and opaque. A look at the microstructure of the residues (Fig. 2-4) helps identify what such reagents were and what different choices were made[ii].A (Fig. 2). The white aggregates visible in cross-section are the remnant of a mixture made of lead and tin calcined and then added to the crucible. This, together with somewhat large grains of sand, would produce the required colour and opacity.

Figure 3. SEM image of residue A showing dark sand grains and remains of lead-tin calx used as opacifying agent.
Figure 3. SEM image of residue A showing dark sand grains and remains of lead-tin calx used as opacifying agent.

B (Fig. 3). Here too crystals can be seen scattered throughout the glass and, like before, these are responsible for an opaque white enamel. However, these are made of tin oxide only, indicating that in this case the calx did not contain lead.

Figure 4. SEM image of residue B showing the tin oxide crystals as opacifying agent.
Figure 4. SEM image of residue B showing the tin oxide crystals as opacifying agent.

C (Fig. 4). There seems to be a third lattimo recipe being tested at the Old Ashmolean. This is more than a simple variant because it used a wholly different type of reagent, the antimony ore stibnite. The glass is indeed rich in antimony oxide while the microstructure reveals small white opacifying particles. These are a compound made of calcium and antimony that form when stibnite is added to the glass and heated. Such recipe is less common in technical writings, but it is reported in Christopher Merret’s commentary to Antonio Neri’s glassmaking treatise.[iii]

Figure 5. SEM image of residue C, showing the small opacifying crystals of calcium antimonate.
Figure 5. SEM image of residue C, showing the small opacifying crystals of calcium antimonate.

From this necessarily brief survey we can see that there is more than one way to make an opaque white glass paste. What is interesting is that such diversity happened at one of the leading chymical laboratories of its time, giving us an idea of the experimental nature of this enterprise. Making glasses was certainly a way of investigating nature, of looking at how transformations come about. At the same time, it was a way to test recipes for the industry. In this sense, artifacts can become a powerful tool for the history of recipes, another way to enter the arena of artisanal knowledge.

[i] Cable Michael 2001, p. 307.

[ii] Neri’s recipes for white enamel can be found in: Cable Michael. The world’s most famous book on glassmaking. The Art of glass by Antonio Neri, translated into English by Christopher Merrett (The Society of Glass Technology, 2001), Book 3.

[iii] For a general survey on glassmaking I suggest chapters from: Janssens Koen (Ed.). Modern Methods for Analysing Archaeological and Historical Glass, 2013.

Umberto Veronesi  is a Ph.D. candidate at the Institute of Archaeology, University College London. His dissertation entitled, “The archaeology of laboratory experiments and early chemistry: Oxford to Jamestown and back” focuses on exploring the practice of alchemy through the lenses of the archaeological materials coming from early chemical laboratories and uses scientific archaeology as a means to inform historical research and questions. Veronesi received his BA in Archaeology from the Sapeinza Universita di Roma in 2013, and his MSc Technology and Analysis of Archaeological Materials from the Institute of Archaeology, University College London in 2014.

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”.