Boiling hot oil: on the assessment of temperature in late medieval processing of linseed oil

By Indra Kneepkens

Indra Kneepkens is a technical art historian, specializing in the materials and techniques of late medieval panel painting. She is currently finalizing her dissertation, which is focused on the use of processed linseed oils and paint additives in the painting practice of the fifteenth and early sixteenth century.

Raw linseed – the basis for linseed oil

From art technological sources, such as recipes and manuals for the preparation of paints, and from the analysis of paint samples, we know that late medieval and early modern craftsmen heated oils for use as a binding medium in paints, as well as for the preparation of varnishes. As a technical art historian, I research and reconstruct these oils and varnishes, to be able to establish the effects they have on paints. My aim is to understand how the development and use of these materials influenced the painting process and the final appearance of art works. Unfortunately, 14th-  to 17th-century art technological sources that include heat-treatment of oil typically do not give absolute temperature indications. This is no surprise, because thermometers were developed in different stages between the late 16th and early 18th century. Therefore, craftsmen had to rely on their senses for the assessment of temperature.

Cennini’s handbook has been transcribed an translated repeatedly, most recently by Lara Broecke in 2015

That controlling temperature was important to late medieval craftsmen is illustrated by a remark in the Libro dell’arte (ca. 1390), that was written by the Italian painter Cennino Cennini. In his recipe for a heat-treated oil the writer almost personifies fire, warning us that it would willingly burn down the house if it got a chance to reach into the pan.[1] And indeed, it seems likely that the temperature of oil was sometimes raised pretty high, to the point where potentially explosive gasses form. So how did pre-thermometer craftsmen determine the temperature of their oils?

Even if not in absolute terms, early modern sources do contain clues about the kind of temperatures that were considered useful in oil processing. In most cases, oils were heated over fire, in ceramic, bronze or copper vessels. As wood or peat fires can easily reach temperatures over 500°C, and the vessels were able to withstand these, it was clearly possible to reach the auto-ignition point of linseed oil (ca. 343°C). Most likely, temperature would have varied from case to case, depending on factors like fuel type and the distance between the vessel and the heating source.[2]

Sometimes sources mention a strong reduction of the oil, or they describe the texture of the end result, comparing it to fluid honey for example. In varnish recipes a string-test reoccurs, in which a finger is dipped into, and then lifted from a cooled drop of the mixture of boiled oil and resins, to see if a thread is formed.[3]My own experiments have shown that to reach a sufficient thickening of an oil or varnish, and to dissolve most resins, the materials must be heated for quite some time and at a fairly high temperature. Finally, empirical tests that remind us of everyday cooking may have been used to keep an eye on the temperature of oils. In Arte de la Pintura (1649), Pacheco describes how bread, garlic and feathers were stuck in boiling oil; if they appeared browned or scorched, the cooking process was completed.[4]

During my experiments over the past few years, it has become evident that one can make a reasonably accurate temperature assessment based on how the oil behaves during heat-treatment. A swirling movement for example, was noticed in oils from a temperature of ca. 90°C, while repugnant fumes typically started to develop around 200°C.

Figure 1. Foam developing on oil heated in a ceramic vessel

I also realized that the development of foam, which is commonly mentioned in recipes, may have been a clear indication of temperature. But it is also closely related to the type of cooking vessel that was used. I did not see any foam until I exchanged my glass laboratory beakers for a glazed ceramic pot. Foam appeared when the oil reached a temperature of 100°C. It must have been caused by water evaporating from the clay body, as I had rinsed the vessel before use. Bubbles also formed when garlic and bread were boiled in oil, from ca. 61 and 80°C respectively, with a high point again around 100°C. Although the garlic started to darken earlier, both bread and garlic clearly browned around 180°C, and completely blackened between 230 and 240°C.

In another experiment thirteen feathers, of different size and from various birds, were dipped in hot linseed oil until they started to curl. Surprisingly, all feathers curled within a range of 27°C, between 237 and 264°C. These experiments not only support the relative accuracy of these empirical methods, but also indicates that temperatures of ca. 100 and 200-250°C were meaningful to early practitioners.

Figure 2. Raw linseed oil (far left) heated at 150 (1-4 hours, jars 2-5 from the left), 200 (8 hours, larger jar) and 300 degrees C (1-4 hours, jars 7-10 from the left).

In more systematic tests, linseed oil was heated to 150 and 300°C, for one, two, three, and four hours. Interestingly, the color and thickness of the oils that were heated at 150°C appeared more or less unaltered after the experiment. In tests where these oils were mixed into paints, they behaved very similar to raw linseed oil. At 300°C the oils thickened and darkened considerably. They affected paints in a very significant way, causing them to level, and making it possible to create smooth glossy films without any visible imprint of the brush. Paints with these oils were also less prone to yellowing. An oil that was heated at 200°C for eight hours however, still made paints level perfectly, but it also caused extreme yellowing.

So knowing how to assess temperature and balancing it over time must have been crucial skills for those who prepared heat-treated oils and varnishes. Experiments have shown that knowledgeable individuals would have been able to make a fairly accurate assessment of temperature, using their senses. They could note changes in the appearance and behavior of oil and indicator materials, and manually test its viscosity. Although there are several indications that temperatures of 200°C and higher were preferred, it makes sense that craftspeople would adapt the temperature to the materials at hand and the desired end result. The lack of unambiguous temperature indications in oil processing recipes reflects this adaptive use of temperature and a reliance on the senses that was expected of craftspeople before the invention of thermometers.

[1]Broecke, Lara. Cennino Cennini’s Il Libro dell’ Arte: A new English translation and commentary with Italian transcription.London: Archetype, 2015, 127, chapter 91.

[2]Aldeias, Vera, Harold L. Dibble, Dennis Sandgathe , Paul Goldberg, and Shannon J.P. McPherron . “ How heat alters underlying deposits and implications for archaeological fire features: A controlled experiment” Journal of Archaeological Science67 (2016): 66.

[3]Broecke 2015, 127. Neven, Sylvie. The Strasbourg Manuscript. A Medieval Tradition of Artists’ Recipe Collections (1400-1570). London: Archetype, 2016: 132-135, no. 92-94.

Banishing the Armpit Goats: Body Odor in Ancient Rome

By Cari Casteel

Cari Casteel is currently working on a manuscript on the social and cultural history of deodorant, based on her dissertation, “The Odor of Things: Deodorant, Gender, and Olfaction in the United States.”Beginning in the fall she will be joining the history department at the University at Buffalo as a Clinical Assistant Professor. You can find her on twitter @thedeodorantone.

Figure 1: Advertisement for Mum deodorant illustrated by Don Herold. Esquire April 1939, 166.

“Remember that night in 1933, Ed Snootz came to the Club Dance with that cave-man aroma? … Just let a man forget himself for one evening and come to a party with a slight case of perspiration fumes and his name is Mr. Goat.” This selection from a 1939 advertisement for Mum—the first commercially available deodorant—reprimanded the fictional Snootz for his body odor.

Many early deodorant advertisementsactively shamed consumers into purchasing their product. Men and women were told that if they did not wear a deodorant it would lead to other failures: in love, friendship, and business. In the case of “Mr. Goat” his faux pas was so egregious that women were talking about it 6 years later.

As I write this from the comfort of my airconditioned office, the outside temperature is 90°F. The moment I venture outside, my body will begin to perspire in order to regulate its temperature. One unpleasant side effect of this perspiration is underarm odor. No need to worry, however, because in the 21stcentury, we have a vast array of deodorants and antiperspirants created to banish body odor.

A commonly held refrain about deodorant use is that because of these scolding advertisements consumers were duped into buying a product to hide perspiration and the accompanying offensive odor. While this is not entirely untrue, it is not the whole story. Mum deodorant was not the first—or even the hundredth—attempt to tone down the “cave-man aroma” described by the ad. As long as people have existed, they have worried about their appearance and smell. While the custom of wearing a commercially produced deodorant is rather new—about 130 years—attempting to combat fetid odor is as old as mankind.

Figure 2: Statue of Barberini Faun located in the Glyptothek Munich. Image credit Wikimedia Commons

The Romans particularly worried about foul body odor and worked fastidiously to keep their bodies clean and smelling pleasant. Just as the Mum advertisement shamed Ed Snootz for his lack of deodorant use, Roman playwrights and poets rebuked and joked about malodorous men and women. This can be seen –and smelled—in an epigram by Catullus:

Rufus, you are being hurt by an ugly rumor which asserts

that beneath your armpits dwells a ferocious goat.

This the women fear, and no wonder; for it’s a right rank

beast that no pretty girl will go to bed with.

So either get rid of this painful affront to the nostrils

or cease to wonder why the ladies flee. (Carmina 69)

Rufus—much like his 20th-century counterpart Mr. Snootz—had failed to practice proper hygiene and as a result could not find a female companion. Throughout Roman texts, foul body odor was described as goaty (hircus) and connotatively undesirable. Roman citizens took pride in their appearance and viewed their perceived cleanliness as a mark of superiority over other civilizations.

In a scene from Plautus’ Pseudolus, two characters gossip about a newcomer from Greece.

Pseudolus: But this servant, who is come here from Carystus, does he smell of anything?

Charinus: Yes, of the goat under his armpits.

Pseudolous: It befits the fellow, then, to have a tunic with long sleeves (2.4.46-49)

Much in the same way that 20th-century deodorant advertisements sought to correct a behavior, Roman prose and poems—such as those by Catullas and Plautus—used satire to poke fun at foul odors, but also as a way to educate and encourage cleanliness. Ovid, in The Art of Love, cautioned readers against offensive underarm odor, writing “I warn you that no rude goat find its way beneath your arms” (3.193). Ovid continued by recommending removing underarm hair and using powders to keep the body free from odor.

The Romans had countless remedies for dealing with perspiration odor. For example, In Natural History,Plinyrecorded a number of solutions for dealing with goats under the armpits. One method for combating body odor was a combination of rue, aloe, and rose oil boiled together and then dabbed on the offending areas (20.51). Another—slightly more fitting—recipe was a concoction made from the ashes of goats’ horns mixed with oil of myrtle, and then rubbed all over the body (28.79). While these solutions might not have checked perspiration, the scented oils would have helped mask the goaty odor.

Most significantly, when it comes to halting foul odors in the 21stcentury, the Romans recorded some of the earliest instances of applying alumen—the main ingredient in many antiperspirants today—as a deodorizer. Roman recipes for alumen as a preparation for halting armpit odor range from, bathing in a mixture of two parts honey and one part alumen, to placing unadulterated alumen stones in the armpits until the odor disappeared (35:52).

For over 2000 years, foul body odor has been a topic of conversation, a location for shame, and a way to assert superiority. Whether in ancient Rome or the present-day United States, dealing with goaty armpits has been a priority for many men and women. If you wear an antiperspirant, next time you apply it, you can thank the Romans.

The devil is in the details: turpentine varnish

Corrosion cast of bronchi and trachea, possibly from a rabbit, sheep, or dog, 1880-1890
Likely prepared by Harvard anatomist Samuel J. Mixter.
The Warren Anatomical Museum in the Francis A. Countway Library of Medicine

By Marieke Hendriksen

One of the first things you learn when you do reconstruction research is that the tiniest detail can make a difference.

Recently, I wanted to prepare an injection wax for corrosion preparations according to a 1790 recipe. Corrosion preparations are anatomical preparations created by injecting an organ with a fluid coloured wax that hardens. The organ is then lowered into a container with a corrosive substance, such as a hydrochloric acid solution, which corrodes the tissue, leaving a negative image of the veins and arteries of the organ. These preparations were made from at least the mid-eighteenth century, but because of their fragility, very few remain. As they were supposedly difficult to make, corrosion preparations were not only a way of studying anatomy, but also a tool for self-fashioning and establishing one’s status as an anatomist.

I have tried to create an injected preparation in the past.[1]It was my first attempt at reconstruction research ever, and although it served me well at the time, now I do things differently.

Most importantly, I want to stay much closer to the original recipe if possible. When we made the injected preparations in 2012, we used modern substitutes for some historical ingredients for economic reasons, and we did not have the time to study every ingredient in detail, substituting those we could not find directly with something we thought would have pretty much the same effect.

The recipe I want to use, Thomas Pole’s 1790 instruction for making a corrosion preparation, calls for a coarse red wax, made from fifteen ounces of yellow bees wax, eight ounces of white resin, six ounces of turpentine varnish, and three ounces of vermillion or carmine red.[2]The wax, resin, and pigment are fairly straightforward.

What is turpentine varnish though? Back in 2012, we ended up using just turpentine rather than turpentine varnish, and although those injections were not meant to be corroded, we ran into numerous problems. For example, it turned out to be almost impossible to keep the wax and the organs at a temperature at which we could both handle it and have it fluid enough to inject. It made me wonder whether sticking with the original recipe could solve that problem, so I set out to recreate it.

This turned out to be more complicated than expected, as there is not one standard recipe for turpentine varnish. Eventually I found a Dutch recipe from 1832 listing a turpentine varnish to finish display cabinets for natural history collections.[3] The ingredients are a pound of oil of turpentine, 8 ‘loot’ (a loot being 1/32 Dutch pound) of white resin, four loot of Venice turpentine, and ½ loot of aloe or kolokwint. Raw larch turpentine has a high concentration of volatile oils that can be distilled. The fluid part is known as oil of turpentine, whereas the residue left in the retort is usually called resin, rosin, or colophony. Oil of turpentine is the essential oil that remains after distilling raw larch turpentine. Venice turpentine is a thick, viscous exudation from the Austrian larch tree, which is not used as a varnish on its own as it becomes dark and brittle when exposed to oxygen and light. Aloe vera is widely known; kolokwint (the Dutch name for Citrullus colocynthisor bitter apple) less so. It is a plant with yellow fruits that resemble small pumpkins, which are very bitter and poisonous. That quality might explain its presence in a recipe for a varnish that is meant to ward off insects. Powdered aloe is readily available from artist’s material suppliers, so I went with that.

The varnish after 10 hours in the sun. The Aloe is the clearly visible murkiness on the bottom. Photograph: author.

The preparation of the varnish was pretty straightforward: put all ingredients in a bottle, cover, and leave in the sun for a day. The only problem was that I had to wait a week for a sunny day. When it came, I put in the ingredients and just left the bottle out in the sun for a couple of hours, which allowed me to stir the ingredients together. The aloe however did not resolve properly, and just sits at the bottom of the jar. While this might not be much of a problem when the varnish is applied to a cabinet, it makes this particular turpentine varnish unsuitable for use in my injection wax. Next time, I will make another batch without aloe and use that instead.

Why do I recount this–admittedly not very exciting–story? It shows how difficult it can be to follow a historical recipe to the letter. It also shows how much you learn from reconstruction research, even if it does not always yield the results you’d like, or as fast as you’d like.

[1]Marieke Hendriksen, Elegant Anatomy, (Leiden: Brill 2015), pp. 1-9.

[2]Thomas Pole, 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), pp. 21-5, 122-42.

[3] S. de Grebber, Over de schadelijke huisinsekten, als de huisvliegen, wespen, muggen, weegluizen, vlooijen, luizen, motten, pels-, boek- en kruidkevers en wormen, hout-, blad- en schildluizen, plantmijten enz., met aanwijzing van voldoende en proefhoudende middelen, om dezelve geheel uit te roeijen, Volume 1,(Amsterdam, 1832), pp. 52-3.

Indigo or no indigo?

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.