The Fire and the Furnace: Making Recipes Work

By Thijs Hagendijk

While working on the Ars Vitraria Experimentalis (1678), the principle book on seventeenth-century glass, I came a across a peculiar remark. The author of the book, the German alchemist and glassmaker Johann Kunckel (1630-1703) composed a commentary on a series of Italian glaze recipes, and somewhere along he dropped the following line: “reproducing this glaze requires as much Art as inventing it” (p. 193). I was struck by this remark and have been thinking about it ever since. What is it that Kunckel tried to tell us here? What does it tell us about recipes, these miraculously concise pieces of text? And how do these written instructions fit into workshop practices? After all, when reproducing a recipe becomes an investment that equals its invention from scratch – why bother with books at all?

That people bothered is in fact beyond dispute. Recipe research from the past years has come up with ample reasons why people engaged with practical texts. People were working on their reputation, tried to organize experiential knowledge, or were concerned about the epistemic status of their crafts. And indeed, all these elements instantly return in Kunckel’s Ars Vitraria Experimentalis. Kunckel is particularly keen on stressing that everything in his book has been vetted through experience. His book reads as an attempt to apply for a good position at the Brandenburg court, and he openly runs down his main competitor, Friedrich Geißler, who worked on a similar book project. “Lieber Herr Geißler, I am sorry that you are so utterly unfortunate in your judgments and comments” (p. 188). In the end, however, we should not forget that the Ars Vitraria Experimentalis was born out of practice. It finds its basis in the workshop, amidst the radiant heat of furnaces, brightly glowing glass, skilled labor and the stinging smell of smoke.

Back to the glaze recipes. While the Italian glassmaker Antonio Neri (1576-1614) originally conceived the glass recipes some seventy years earlier, Kunckel now presented a German translation of these recipes, lavishly annotated with his comments. In an attempt to better understand how this concoction of recipes and commentaries would fit into actual workshop practices, I teamed up with Márcia Vilargiues (Universidade NOVA de Lisboa) and Sven Dupré (Utrecht University) to rework a couple of recipes. We gathered and prepared the ingredients and spent days around furnaces trying to reproduce the recipes.

Figure 1. One of the wood-fired furnaces we used to reproduce the glaze recipes. Note that the fire is stoked from the sides. Location: Telheiro da Encosta do Castelo, Montemor-o-Novo, Portugal.

We dragged wood, stoked furnaces and patiently waited for the heat to come. We tried to control the smoke and played games guessing temperatures from different shades of bright orange. Showers at the end of the day invariably turned my white bathtub into a deep brown. During these days, our main occupation was fire. Ingredients for the glaze, their quantities and the order in which they had to be combined became mere side issues.

Figure 2. The furnace opening was closed with bricks to keep in the heat. Bricks were only temporarily removed to move samples.

It was in this smoky atmosphere that we began to see a fundamental characteristic of Kunckel’s commentary. The focus of commentaries, annotations and marginalia in practical texts had traditionally been the testing, correcting and improving of recipes, but Kunckel took a slightly different approach. He started to dress up Neri’s recipes in his commentary and added new and previously unarticulated layers to the original recipes. What layers? Well, think for instance about the role of fire. While Neri straightforwardly communicated ingredients, ratios and the different steps in his glaze recipes, nothing prepared us for the important task that fire management turned out to be, which went far beyond sending some wood up in flames. Kunckel, on the contrary, emphasizes this very issue in his commentary, and repeatedly argues that “the Fire is the principle thing to observe” (p. 194).

Figure 3. To work efficiently, we reproduced several recipes at once.

Indeed, while working with different furnaces, we learned that furnaces are more than simple and inert providers of heat. Instead, wood-fired furnaces become a tool by which the quality of the glass is shaped in addition to the ingredients and the quantities prescribed by the recipe. Temperature, atmosphere and position in the furnace are all partly responsible for the end result. In the end, reworking the same recipe in three different furnaces left us with three sets of glazes in different qualities. See how Kunckel cleverly shifted the perspective in Neri’s recipes? Kunckel made his readers aware of the circumstances they had to navigate when putting a recipe into practice, something for which Neri left them unprepared.

Figure 4. Two samples of the red roischiero glaze.

Making processes can be understood as processes of growth, the anthropologist Tim Ingold tells us. And this stance on making has significant consequences for how we understand the position of texts in these processes. Makers stand in an ecological relation with their environment, their materials, tools, and the forces they work with. To make a glaze means that the molten glass, the furnace, the smoke, etc. act in correspondence with an observant and anticipating glassmaker. Crucially important here is that ideas, designs or written instructions cannot simply be imposed onto reality. Recipes need to become part of it instead. To make something means to adapt and respond to the local and unique joining and intertwining of forces, materials and elements – and written instructions form just one strand in this creative process. Seen in this light, Kunckel’s remark was not so much a pessimistic note on the possibly superfluous nature of glaze recipes, but rather a reminder that reading and reproducing a recipe is an all-encompassing effort to make the recipe work in the unique constellation of the individual workshop. Reproducing a recipe is reinventing the wheel.


Thijs Hagendijk is a lecturer at Utrecht University. Earlier this year, he defended his dissertation on reading and writing practices in the early modern arts, with a specific focus on text usage in historical glassmaking, painting and metalworking. He works on the intersection of technical art history and the history of chemistry, and is interested in performative methods, such as reworking, re-enacting and reproducing historical techniques, materials and processes.

*You can read more about this project in Thijs’ recent article in Ambix.

Colouring metals in the Far East

By Agnese Benzonelli

How far can someone go in the name of research? In my case quite a long way. For a month, I loosely taped tiny plates of metal to my hands and woke up every morning with green stains on them. I was investigating craft recipes employed in the far East since the fourteenth Century to create coloured metal and alloys used for beautiful small artefacts. Whereas Western taste preferred the natural colour and the polished lustre of metals, the Eastern preference was to use the process of chemical patination, where different chemicals react with the surface of copper and copper alloys to form new coloured compounds.

Fig.1: Left: a tsuba (handguard of Japanese sword) made of shakudo and gold; BM-TS244. Right: a Chinese gu-tong box; BM-1992,1109.2. Photos made by A. Benzonelli.

The Japanese created a whole class of coloured alloys, called irogane. They added small amounts of different elements to the copper and simmered it in a solution containing copper salts, alum, vinegar and other ingredients, to form coloured patinas on the surface. The most beautiful patina, shakudo, was made with copper and gold and achieved a deep blue-black colour. Combining a variety of alloy compositions and solution ingredients, they were able to create hues ranging from pale brown to black. Inlaying different irogane, gold, silver, and lacquers, they were able to create small artefacts and swords fittings with complex and visually impressive designs and patterns.

Fig.2: Picture of the 13 Japanese solutions created and tested taken from Japanese recipes reported in Eastern books.

Later on, Chinese craftspeople imported the technique from Japan, possibly through travellers or trying to copy the Japanese artefacts, and, from the Ming period (1368-1644), they used it to colour ink or tobacco boxes. In contrast to the Japanese irogane, the Chinese would patinate a gold-silver alloy only, which resulted in a dark colour similar to that of shakudo, which they called gu-tong. In both cases, the precious metal content was 1-3%, a larger amount would not affect the final patina colour.

There’s not a lot known about the two different recipes the Chinese craftsmen employed to produce their patinas. However, we do know that one process they utilised was similar to that used by the Japanese to produce the irogane,butwe have no precise recipes for the solutions. Another involved handling the metal until the perspiration from their hands corroded the surface.

Creating and play with metal colours has always fascinated me. Why using gold and silver to achieve that dark colour, instead of cheaper alternatives? What was the role of the different ingredients used in the recipes? Could sweat really be used as a patinating solution? Why did Japanese recipes tell not add precious metals to bronze (copper alloyed with tin) but only to pure copper? Could it be confirmed through scientific analysis that the technology was really transmitted from the Japanese to the Chinese culture? To find answers, I needed to conduct a systematic experimental research which could explain the reasons behind the technological choices of Japanese and Chinese craftsmen.

 I reproduced a series of alloys with tin, gold and silver, which I then patinated, following the recipes for shakudo and gu-tong from available texts. These are not numerous, as the recipes were mainly kept as secret and passed from father to son. We have city records, information sheets given by dealers and, in Japan, technical texts on metal working. I analysed the resulting patinas with techniques borrowed from modern material science, and used the experimental data as reference for the interpretation of historical patinated artefacts in museum collections.

I found that, for both the Japanese and Chinese recipes, the presence of gold in the alloy did, in fact, change the colour of the final patinas, which resulted in a better, more uniform and darker hue. I also noted how parameters such as the fine grade of surface polishing prior to the patination, the use of tin-free alloys, the selection of copper acetate as a main ingredient and the addition of vinegar are all processes and actions that led to a reduced patina growth. And as it turned out, sweat was indeed an effective patinating solution in the Chinese patination (as it can be noticed by the green corrosion products left on the hands), but the presence of gold in the alloy composition is nonetheless essential to obtain a dark hue, not achieved in gold-free alloys. Sweat is a slightly acidic solution, similar to that of used by Japanese craftsmen, essential to create a coloured copper oxide on the surface in just 48 hours of handling. Similarly, in both technologies cleaning of the alloy before or after the procedure suggested in Japanese texts and the abrasive action of the hands in the Chinese method are both similar and crucial steps in the patination process. I concluded from these findings that a dark patina was not the only feature that the craftsmen of both cultures had been striving for. They also seemed to be after a shiny appearance, given by the metallic lustre coming from the alloy.

Fig. 3: Alloys of different compositions patinated with Chinese patination.

In combining experimental and historical observations I gained an understanding of the intentions behind the technological choices made by the Japanese and Chinese artisans. My analysis confirmed the deliberate nature of these choices made to achieve dark and shiny blue-black colours otherwise impossible. This confirmed the importance of colour as a driver of these artisanal processes, and supports the idea that the knowledge was transmitted between the two cultures.

Was it worth in the end – the green hands and other discomforts suffered in the name of research? It was the first study to provide a scientific basis to our knowledge of the methods and choices made by those people, the ingredients they employed in making dark patinated artefacts, and contributed to our pool of knowledge of the artisanal methods and practices described in historical sources. So yes, it definitely was, and I would definitively do it again.

Revisiting Marieke Hendriksen’s Indigo or no indigo?

Today we revisit a post written in pre-Covid-19 times, when borders were open, planes were flying and we used to travel the world. In this post from 2018, Marieke Hendriksen recounts how her holiday in Laos offered opportunities to learn more about indigo and the local dyeing processes. Elaine Leong


Marieke Hendriksen

Fermenting indigo at Ock Pop Tock, Laos. January 2018.

When you say indigo, the first thing many people will think of is blue – jeans blue. (Or if you’re me, you’ll think first of a seventeenth-century recipe to make decorative blue prunes from wax with indigo. Occupational deformation.) But historically, indigo has been used in many more ways, and to make more dye colours than just blue, as I recently discovered. Today, most jeans are died using a synthetic blue dye, but indigo dyes, made from some of the over 750 species of the genus Indigofera as well as from some other plants, have been used to dye textiles for at least 6,000 years, while other subspecies of Indigofera were traditionally used as analgesics with anti-inflammatory properties.

The term ‘indigo’ according to the OED started to occur from the sixteenth century onwards in various European languages to denote blue dyes from India (or east Asia more generally), but can now also refer more generally to dyes, violet-blue light, or blue hues. It might be argued that the term only really applies to dyes created from Indigofera subspecies, while it could also be said that indigo is any dye created from plants through the decomposition of the glucoside indican, which exists not merely in the indigo-plant, but in woad and various other plants too.

Wash the freshly picked leaves…

While on holiday in Luang Prabang, Laos, I took a weaving and dying workshop with Ock Pop Tock, an organization that was established to preserve the traditional Laotian craft of making hand-loomed textiles. There, I discovered that there is more indigo besides Indigofera, and that one indigo plant can give many more dyes than just blue. They also have a wonderful informative website on natural dyes. At Ock Pop Tock, the plant species used to create indigo dyes is Persicaria tinctoria, or long leaf Japanese indigo, a plant indigenous not to Japan but to China, Vietnam, and Laos. Depending on how the leaves are treated, it can be used to create blue, green, black, and mauve.

…give them a good pounding to create a dye.

Using the fresh leaves creates a green dye, fermenting them for at least five days and adding limestone as a mordant gives a blue dye. Traditionally, the Lao believed that the dye was female, and that it fermented because it attracted a male spirit. To coax the spirit, the pots containing the dye would be dressed in a skirt, and a knife placed on top of the lid to ward off evil spirits that could ruin the dye. The fermentation is actually a naturally occurring oxidation process, with atmospheric oxygen as the oxidant. Regular stirring ensures the process continues. The longer the indigo mixture is left to ferment, the darker it turns. If this mixture is boiled, it turns black. Alternatively, a rare indigenous plant, mak bow or bow vine, can be added to the blue dye to create mauve.

The end result: a beautiful scarf

As part of the half-day workshop, I got to dye a silk scarf with a dye of my choice. I love green hues and wanted to make a dye from start to finish, so I chose to dye my scarf ‘indigo’ green. This was, apart from some pretty intense pounding of leaves, surprisingly easy. I got to pick fresh Persicaria tinctoria leaves in the beautiful garden, washed them, and mashed them vigorously in a mortar for about five minutes. Then I transferred the mashed leaves into a tub, added some cold water and then the raw silk scarf. After kneading the dye into the fabric for a couple of minutes, I could rinse my scarf and hang it to dry. The end result is a beautiful soft green scarf, that is not just a souvenir, but a tangible reminder of the traditional Laotian knowledge about natural dyes preserved and shared at Ock Pop Tock.

Revisiting Erik Heinrichs’ The Live Chicken Treatment for Buboes: Trying a Plague Cure in Medieval and Early Modern Europe

Today we revisit a post originally published in 2017 by Erik Heinrichs on a seemingly odd treatment for plague buboes: the feathers from a chicken’s backside. Erik notes that there is a very long history of using chickens and chicken broths in medicine, partly because chickens are such commonly kept animals. I certainly remember being fed chicken broth when I was ill as a child, but I must say that I broke that tradition with my children. They still get ice cream though… Laurence Totelin


By Erik Heinrichs 

Titlepage of Philippus Culmacher’s plague treatise, Leipzig: circa 1495
Credit: Wellcome Library, London.

While researching German plague treatises I became fascinated by one odd treatment for buboes that appeared again and again, despite sounding so far-fetched. One sixteenth-century version calls for plucking the feathers from around the single hole in a chicken’s backside, then placing it on a person’s bubo. The instructions say to hold the chicken on the bubo until it dies, when it must be replaced with a new chicken, similarly plucked. I soon dubbed this the “live chicken treatment for buboes” and after years of casual encounters I began to track the recipe more systematically. As strange as it sounds, versions of this “live chicken treatment” were fairly common in plague writing, beginning with the Black Death and lasting, amazingly, into the eighteenth century. Tracing the long history of this recipe led me to explore questions such as: Where might this come from? Why chickens? Why might healers think that this was a good idea? Did anyone actually try this or is this all theoretical? As a historian, I was also interested in change over time within the recipe. Here I found much to explore, as I followed the recipe’s twists and turns over a seven-hundred year period, roughly 1000 to 1700.

The “live chicken treatment” turns out to have a long history, indeed. Its origins seem to lie in Avicenna’s Canon of Medicine, although it may be older than that. Chickens and chicken broth were a common source of medicine in early times, probably because chickens were such ubiquitous and useful animals since antiquity. Not only did Avicenna praise chicken broth for its general benefits for the body, but he also recommended placing a cut chicken on a poisonous bite or sting in order to fight poisons. In later centuries European physicians turned to Avicenna’s advice when they faced the mysterious and devastating epidemics of the fourteenth century. As Europeans emphasized the poisonous nature of the plagues around them, older treatments for poisons drew new attention. The first mention of using a chicken rump to draw poisons out of a bubo appeared in the very first plague treatise of 1348, coming in response to the so-called Black Death. Here the Catalan author Jacme d’Agramont seems to have introduced a novel and lasting adaptation of Avicenna’s recipe, although the “cut chicken” version persisted in plague treatises for centuries to come.

Most interesting for the history of trying and testing cures are the many variations of the “cut chicken” and “chicken rump” versions of the treatment, as well as physicians’ comments about how effective they are. Especially after 1400, physicians seem to be thinking about this recipe quite often as they seek practical treatments for the plagues of the time. Physicians were preoccupied with altering the recipe in order to reason out the nature of the mysterious poisons underlying the plague. Some add substances to the process, such as salt placed on top of the chicken as it is placed on the bubo. During the fifteenth century, a number of German physicians began to explain the treatment’s workings in a strikingly physical way—that the chicken breathes through its backside and thus pulls the bubo’s poisons into itself. This change led to the suggestion to hold the chicken’s beak shut during the treatment in order to force the chicken to breathe from below. My article (accessible here) show how all aspects of the treatment changed over time as physicians engaged with the recipe, including the quantity of chickens used, the amount of time required, and even the type of animal in question. This work demonstrates the importance of the recipe itself as a platform for thought, experimentation, and communication among physicians.

Perhaps a surprise to modern readers, many physicians praised their version of the “live chicken treatment,” describing it as effective and desirable. Such comments multiply after the introduction of print, which encouraged the production of plague treatises, some fitted with fetching cover illustrations for the marketplace (see image below of Philippus Culmacher’s treatise of circa 1495). In German-speaking lands especially, sixteenth-century physicians used their printed plague treatises to promote their own services and expertise at a local level.[1] This brought about a change in the genre whereby physicians seem more eager to discuss their own experiences with effective recipes in order to appeal to the practical interests of a broad audience. Amidst this change comes evidence that some German physicians witnessed first-hand the successful use of the “live chicken treatment.” Another interesting change during the sixteenth century is the increased attention to the bodily warmth of the chicken as the treatment’s active healing force. These emergent views provide a tantalizing link to modern medicine, since moist heat remains one of the treatments for buboes today. For more information, please read my article.

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[1] For a survey of German plague treatises from the first century of print, see: Erik A. Heinrichs, Plague, Print, and the Reformation: The German Reform of Healing, 1473-1573 (London: Routledge, 2017).