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.


3 thoughts on “The devil is in the details: turpentine varnish”

  1. Dear Marieke,

    I find your ‘not very exciting’ story quite interesting!

    I had never heard of the technique of corrosion casting. Hence, I am unfamiliar with what kind of physical properties are required from the finished recipe to be suitable for corrosion casting…I’m just curious.

    I wonder whether the only reason you find your reconstructed recipe unsuitable is because the aloe wasn’t dissolved properly?
    If so, did you have confirmation of the botanical origin of the aloe species you bought? Or did you harvested it yourself?

    I pose this question because I know from our research project that fraudulent practices are a common thing in today’s natural substance trade. The many commonly used artist materials we bought were sold by their trivial and did mention their botanical name . Only after organic analysis it became apparent that for example sandarac, several copal species, turpentine types and colophony were often adulterated (not pure) or from another botanical origin.
    After contacting the suppliers, they themselves were unaware of the product’s quality they are buying. It is a trade mainly based on trust, just as it went in the past.
    On some occasions these suppliers receive a kind of ‘certificate’ that should prove the product’s botanical origin but its legitimacy is often ambiguous.
    Also, their is a large gap between the harvesting companies/families/individuals and the supplier, with several middleman, making adulteration profitable and therefore tempting.
    I don’t know how different the chemical composition is between aloe different species and whether this could affect the outcome? Although I did some preliminary rheological tests on our true sandarac (tetraclinis articulata) sample and a ‘sandarac’ sample from an unidentifiable botanical origin. Despite their chemical differences, both products’ rheological behaviour was similar. Hence, at least from the materials’ flow perspective, there was little difference…

    The recipe itself mentions decanting the liquid when there is a brown layer at the bottom. I know for lacquer recipes that the complete dissolvement of the ingredients is not necessarily a requirement. For example, not all copal species dissolve completely in spirit. In some cases the author mentions this and states that one should decant the clear part from the undissolved parts and the dross.

    Really interesting work and topic!

    Yours,
    Vincent

  2. Dear Vincent,

    Thank you for sharing you thoughts on this, and my apologies for my slow reply. You are absolutely right that the failure to dissolve may have something to do with the quality / purity of the Aloe. I bought it from Kremer artist supplies in this case, but by the end of the year I should have access to a tested sample from an old botanical trade collection, so then I will be able to compare them. For now, I will indeed just decant the liquid and use it like it is in my experiments this summer. To be continued!

    Very best, Marieke

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