On Mordants of Splendor
Please cite as: Jan van Daal. 2024. "On Mordants of Splendor." Last updated: 14-06-2024. https://story.durare.eu/on-mordants-of-splendor.
Art technological recipes can help us understand which materials and techniques artisans in the past used to make artworks, how people thought and wrote about art, and what they valued in art.
However, for us today it is not always clear what these texts aim to communicate and to whom. A trial-and-error approach through repeated hands-on experimentation can help us to better understand what these texts do and do not say.
In this blog, I recount what we learned from experimenting hands-on with a set of three early medieval recipes for the first time.
Three recipes for gold leaf mordants
An early medieval Latin text titled De diffirentia exaurationis ('On different ways of gilding') provides three recipes for gold leaf adhesives. The text does not provide a name for these adhesives, but in art historical jargon we call them 'mordants', which derives from the Italian mordere, meaning 'to bite' or 'to nip'.
I am interested in De diffirentia as part of my PhD research on splendor in medieval art. I find De diffirentia so interesting because its recipes instruct to tint the mordants with saffron, a spice derived from the stems of the Crocus sativus flower. Throughout history saffron has been an exceptionally costly spice – and it still is.
These mordants served as adhesives for lustrous gold leaf, but adding saffron would have made the mordants themselves splendid and costly materials too. What would it be like to make and work with such splendid adhesives?
The experiment
The experiment of making and working with these saffron-infused gold leaf adhesives was part of the interdisciplinary Lorentz Center workshop Gold & Mercury | Metals in Transit in the summer of 2022. After discussing the chemical and artisanal history of gold and mercury, we came together with a group of 11 scholars in the Utrecht University ArtLab.
I had previously reworked the De diffirentia recipes into three hands-on experiments. We split into teams to tackle each of my translations of the mordant recipes from De diffirentia.
Experimenting together stimulated exchange. By the end of the day, each subgroup formulated their own aspect of the text that they found puzzling or inspiring. We shared those areas of interest to come up with ideas for more comprehensive studies of De diffirentia in the future.
Warming
The first subgroup worked on a mordant made of almond gum, water and saffron. They had to warm the mordant, but how do you translate a Latin verb for warming (tepefacere, in this case) into practice? They found that heating the mordant too much reduced its adhesive strength.
Color
The second subgroup made a mordant of egg white and saffron. Their main challenge was to work out the color of the mordant. They found out that, while the text offers no point of reference, with saffron alone you can achieve a range of hues that may qualify as 'yellow'.
Stickiness
The third subgroup made a mordant of almond gum, saffron, water and linseed oil. They were mainly interested in the stickiness of this mordant. By following the recipe literally by using pure linseed oil – and failing to produce a working mordant – they realized that there is often more than meets the eye when it concerns historical recipes.
How to read this story
In the following chapters of this blog I explore my translation of the recipes from De diffirentia and show how each subgroup approached one of three key themes: temperature, color and stickiness. You can jump to any of these themes by clicking the respective chapter titles in the banner at the top of your screen.
In the next chapter, for which you can keep scrolling, I provide some more background information about De diffirentia and the translation of the recipes.
The recipes
De diffirentia exaurationis or 'On different ways of gilding' is first attested in an early medieval recipe collection known as the Compositiones tradition. The Compositiones is part of a manuscript codex, no. 490, kept at the Biblioteca Capitolare Feliniana, Lucca, Italy.
There are 10 manuscripts in the Compositiones tradition that contain De diffirentia. As the Lucca manuscript is the oldest surviving one, I started my investigation based on this text.
Here you see my English translation of De diffirentia. Click on the text to unfold the Latin transcription made by Hjalmar Hedfors in 1932.
On different ways of gilding
Different ways of gilding. If on wood: almond gum steeped for one day. Next, you will profitably rub it together with water and add saffron, as much as suffices, tint that gum-water; and once everything has been warmed over a gentle fire, for that was necessary, employ it on wood. – On cloths or on walls: take unbeaten egg white and add saffron, as much as suffices, tint, and after it has been mixed together and whisked, store it in a glass jar. – Linseed oil I part, soaked gum I part, saffron, as much as suffices, mix together and decoct with water.
[Consult] these three chapters, where it is necessary to work in gilding with leaves.
De dif<f>irentia exaurationis
Diffirentia exaurationis. Si in ligno, gumma amigdale [in] infusa die una. Deinde teres utiliter ipsam cummam cum aqua et addito grogum, quod sufficit, tingue ipsam aquam cum gum<m>am; et tepefacta omnia lento igni, ut necesse fuerit, operari⌜t⌝ in ligno. – I<n> pannis vel in parietibus tollis albumen obi subtile et addito grocum, quod sufficit, tingue et commixta et trita reponis in vaso vitreo. – Lineleo<n> ·/· I, gumma<m> infusa<m> ·/· I, grogum, quod sufficit, comisce <e>t cum aqua dequoque.
Ista tria capitula, ubi necesse⌜t⌝ est in exauratione petalarum operare.
Its title notwithstanding, the text devotes almost no attention to gilding in general. The text instructs on how to make the mordants and informs what substrates you should apply them onto. It does not instruct on how to prepare these substrates, how to apply the mordants and how to lay on the gold leaf.
This is an important clue towards understanding the meaning of De diffirentia. Recipes for making gold leaf and preparing substrates for gilding in fact feature elsewhere in the Compositiones.
De diffirentia seems to be aimed at an experienced audience – people familiar with these materials and applying gold leaf. As first-timers experimenting with making these mordants we were able to confirm this hands-on.
Temperature
Two of the mordants contain gum from the almond tree (Prunus dulcis). The almond tree produces this gum as a defense mechanism to injuries and disease.
Almond gum largely consists of polysaccharides, long chains of carbohydrates, like cellulose. When reacting with water, they break up into monosaccharides (simple sugars) and oligosaccharides (polymers of a few simple sugar units).
These sugars give the sticking strength to the mordant made of almond gum, water and saffron.
The group that worked on the almond gum mordant for use on wood faced the question how to assess the temperature to which the mixture of almond gum, saffron and water should be heated. The recipe specifies to ‘warm everything over a gentle fire’ (tepefacta omnia lento igni).
It proved a challenge to translate this ancient instruction into a specific temperature using a hotplate. As we now know from materials science on almond gum, its solubility in water increases with temperature, owing to the polysaccharides bonds breaking down under the influence of heat, starting from about 30 °C.
The group settled on a temperature of 50 °C and succeeded in producing an almond gum-water-saffron solution. They brushed this mordant onto prepared wooden panels and succeeded in overlaying it with gold leaf, as you see here:
However, when we touched the mordant itself to assess its sticking strength, this was surprisingly disappointing. As it dried on the panel – which it quickly did – it hardly left a sticky residue for the gold leaf to adhere to.
This suggests that not only do the Latin words for temperature here probably indicate a lower temperature range, but also that the composer of this recipe expected their audience to be able to infer the correct temperature from the materials specified in the text.
Color
The group working with the egg white and saffron mordant for use on cloth and walls experimented with color.
Egg whites are used as the adhesive for the gold leaf. The recipe instructs the tinting of the whites with saffron, a seemingly simple procedure.
However, a clause that features in all three recipes puzzled the group: the texts indicate a saffron measurement of, 'as much as suffices' (quod sufficit).
The group pushed the tinting as far as they could. As expected, they found that they could tint the egg white a golden yellow.
This piqued the question what quod sufficit means. On the one hand, this clause seems to imply that the person making the mordant could pick from a range of 'yellow' hues at their discretion.
On the other hand, the fact that quod sufficit features in all three recipes suggests that the importance of the mordants' color lies at the heart of what De diffirentia aims to communicate.
Stickiness
The third group worked on a mordant also for cloth and walls, made of almond gum, linseed oil, water and saffron. Their main challenge was to assess the stickiness of this mordant.
The recipe instructs to 'decoct' (dequoque) this mixture, implying heating to 100 °C or higher. As I explain in the chapter on temperature, this would diminish the sticking strength of the almond gum. Thus, somehow the linseed oil would have to be the main contributor to the stickiness of this mordant.
However, what kind of 'linseed oil' does the recipe refer to? While this may be pure linseed oil, the recipe following De diffirentia in the Lucca MS is a recipe for 'linseed oil', which is actually a linseed oil based varnish. As it contains gum and resin, this varnish would definitely have been sticky too.
Linseed oil is often a component in gold leaf mordants. As a 'drying' oil, the components in linseed oil crosslink (or, polymerize) over time under the influence of oxygen. This creates a firm ground for gold leaf to adhere to.
The group followed De diffirentia literally and use raw linseed oil. After decocting the water, they were left with a tinted oil.
The group expected something sticky, but found that the substance they produced had little adhesive strength. Since, according to the recipe, we were producing a sticking substance for adhering gold leaf, the stuff the group produced did not meet their expectations.
It is likely, as other recipes for this type of mordant suggest, that the linseed oil referred to in the De diffirentia recipe was treated in some way to make it more sticky. This could have been done by heating it, by exposing it to the elements or by adding a resin to it. In any case, there is more to this recipe than meets the eye.
Takeaway
The mordants in the recipes we experimented with derive their splendor from a precious ingredients like saffron, and/or from their material and technical excellence as a glue for precious gold leaf.
Our hands-on experience with these recipes generated new questions about the making (cooking temperature) and appearance and handling properties of mordants (color and stickiness). As such, our experiments generated fundamental new entry points into reconsidering not just the meaning of the ancient texts we studied, but also the complex relations between mordants and splendor.
Further reading
This section offers some online resources for further reading on the main topics that feature throughout this blog.
On gold and mercury:
Gold and Mercury: Amalgamated Histories in Chemistry, Culture, and Environment, an Ambix (vol. 70, no. 1) special issue following the Gold & Mercury | Metals in Transit workshop.
On saffron:
The Cambridge Saffron project, a cultural history of saffron (mainly) in England.
On almond gum:
Bouaziz, Fatma, Mohamed Koubaa, Khawla Ben Jeddou, Fatma Kallel, Claire Boisset Helbert, Anissa Khelfa, Rhoudha Ellouz Ghorbel, and Semia Ellouz Chaabouni. 2016. 'Water-soluble polysaccharides and hemicelluloses from almond gum: Functional and prebiotic properties.' International Journal of Biological Macromolecules 93(A): 359-68.
Hosseini, Ebrahim, Hamid Reza Mozafari, Mohammad Hojjatoleslamy, and Esmat Rousta. 2017. 'Influence of temperature, pH and salts on rheological properties of bitter almond gum.' Food Science Technology 37(3): 437-43.
On the Compositiones tradition:
Brun, Giulia. 2015. The transmission and circulation of practical knowledge on art and architecture in the Middle Ages. The case of Compositiones Lucenses tradition and its connection to Vitruvius’ De architectura. Ph.D. diss, Politecnico Milano.
Frison, Guido, and Giulia Brun. 2018. 'Compositiones Lucenses and Mappæ Clavicula: two traditions or one? New evidence from empirical analysis and assessment of the literature.' Heritage Science 6(1): 1-17.
Credits
Workshop participants:
Dagmar Beyaard
Donna Bilak (Visiting Assistant Professor, School of Art, Pratt Institute, dbilak@pratt.edu)
Marjolijn Bol
Emma van Duin
Hannah Elmer
Sanne Frequin
Manouk Jacobs
Grace Kim-Butler
Karline Lace
Clara Mikellides De Chiaro
Workshop organization:
Marjolijn Bol
Jan van Daal
Grace Kim-Butler
Clara Mikellides De Chiaro
Photography:
Grace Kim-Butler
This workshop was part of Dynamics of the Durable: A History of Making Things Last in the Visual and Decorative Arts (DURARE). The ERC DURARE project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 852732). The workshop was organized as part of the Lorentz Center workshop Gold & Mercury | Metals in Transit, 7–10 June 2022