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Gum Tragacanth (and early marbling trials)

Early marbling trials look promising.  This is from trial series #7, made from brazilwood, buckthorn and turmeric, animal coal, charcoal ash, and ox-gall, among other things.  Doing the marbling has helped verify the number of pigments on the page (three, plus gall), and their origins.

Over the past few weeks, I’ve been writing up grant and fellowship proposals– or, maybe I should say “not writing them up,” since I’ve been finding ways to be productive while avoiding the task.  (Among these strategies of avoidance are my first marbling trials– of which more below.)  Doing a fellowship proposal means seeing a project from above; it means understanding its stakes and impact, or, at least, being able to pitch stakes and impact.  But the whole project of The Motley Emblem has been predicated on the opposite approach– that, if we just attend to the details, the picture will emerge on its own.  I’ve generally found that to be true in my own work, which is one of the reasons I was attracted to marbling in the first place.

Anyone who has been reading around in this website, or has run across it before, knows that my curiosity gets easily captured by situations where the whole clearly exceeds the sum of its parts.  Since this is most situations, I’m easily captivated– but some things make that mismatch more manifest than others.  I also like situations where the whole is far, far, less than the sum of its parts– or, better yet, both: both more and less.  I like all that energy lavished on something small, but, also, when the something small is different than any of the parts could have known.

Marbling is just such an art, where the total effect, which either does or does not resemble the veins in marble, emerges entirely by the careful handling and complex interactions of chemicals in mixture.  This is what we mean by “emerge”– a word which I was pleased to find some years ago is itself a legacy of early modern chemistry.  “Emerge” is just the opposite of “submerge”; it means to rise from a liquid.  But, for a few people in the 1650’s, it started to name the appearance of things in mixtures, as though they rose from a liquid– and sometimes even when they arose in a liquid, like the red color that could be made by adding an alkali to senna tea.  The marble emerges from the right combination of chemicals– which, in themselves, have no quality of marble about them.

Tragacantha vera, “The True Goates Thorn.” Tragacanth was sometimes called “gum dragon,” vestiges of which are possibly to be seen in the rendering of the sweeping root structure. Image from John Parkinson, _Theatrum Botanicum_ (London: 1640), 999.

Gum tragacanth is an exudate from a handful of shrub-like legumes growing in Macedonia, Anatolia, and now the greater region of Mesopotamia.  They have been cultivated there for nearly a millennium– but not for their berries, which are inedible, or their lumber, which is too stunted to be of any human use.  They are kept solely for their defense mechanism.  When one of these stubborn, thorny little shrubs is cut– especially when its roots are damaged– it exudes a gummy sap, which hardens to close the wound.  The thing is, if you grind this gemlike exudate, and put it in water, it quickly swells into a thick gelatin, like tapioca.  I can tell you from experience that it doesn’t take much.  One part in a hundred is enough to make a thick starch; three is enough to make something almost like jello; five makes a thick sludge that has to be painstakingly broken up just to be disposed of.  That’s tragacanth, having the last laugh.

Tragacanth is what is called a mucilaginous hydrocolloid– mucilaginous, because it belongs to the roots of a plant, and hydrocolloid, because it is a macro-molecule which is easily suspended in water.  Mucilage is a substance found in most roots to some degree; it evidently helps roots stay in contact with the soil, forming a sort of crust between the root and the earth, such that if the soil dries out and contracts, the root nevertheless clings to it.  In some plants, it is also found in root, branch, and stem; here, it seems to serve a defensive function, healing up places where the plant is cut.

Now one of the major exports of Iran, where most tragacanth is cultivated, it used as a thickener in foods and pharmaceuticals, as a dressing agent in textiles, and as a binder in specialized artists’ materials, like pastels.  In marbling, it is added to water to form the thick, syrupy substrate upon which pigments are spattered; the thickness of the substrate, called “size,” helps keep the pigments on the surface of the medium, where they can be taken up by paper, wood, or leather.  Many gums would serve the same trick.  Beginning in the mid-nineteenth century, marblers began using an extract of a sort of moss-like red algae called carrageen, which is yet more forgiving than tragacanth, and I have it on good authority that gum Arabic can be substituted in a pinch.  That tragacanth was favored for hundreds of years is strictly a matter of historical contingency.  Marbling was from the middle-east, and Tragacanth was, too.

Joshua Reynolds’s portrait of Suzanna Beckford, in a watered-silk gown. Beckford was heiress to a massive sugar fortune. Reynolds attempts to achieve the moire effect of watered silk with only Prussian Blue and Venice White Lead. Image from Tate.

The reason for the perfection of this curious art in Turkey, rather than elsewhere, was noted by the earliest tourists to witness it being done.  John Sandys, visiting the Sultanahmet region in Istanbul, compared the result of the art to watered silk– another emergent pattern, this one called “moire“–and remarked that it was popular in Turkey because of the proscription against figural art in Islam.  Though the popularity of marbling in Europe benefitted from an association between veined marble and classical sculpture and architecture, this resemblance is not what accounts for its form; in Turkish, no allusion is made to marble at all, and the paper is merely called ebru, “clouded” or “speckled.”  Rather, what appealed to the European taste was the art form’s nonfigurative aesthetic, which was unusual in a tradition that tended to approve of art as the expression of a design or an idea.

The best description of marbling from the eighteenth century is Robert Dossie’s, but his instructions for preparing the size are perfunctory– we are only to achieve a consistency similar to the mixture of gum Arabic and rock sugar used for watercolors.  But adding a similar amount of gum– roughly one part in 24– proved to be way too much.  Just one gram per 100ml of water appears to be about right: thick enough to support the pigments, but not so thick as to form a gloppy paste that sticks to the paper.

A sample from trial #8, which, like the previous one, is rose-pink, Dutch pink (yellow), and a mixture of Dutch pink and Prussian Blue.

I can’t share photos of the gums, here: there’s nothing to show, since it looks like slightly hazy water.  But I can share some early results, a few trial runs at marbling with rose pink, Dutch pink (which is yellow), and a green made from Dutch pink and Prussian Blue.  Seeing the pigments on the page is strong evidence that these were Sterne’s pigments, as well– though only further writing-avoidant behavior (perhaps involving a strong microscope) can make the determination certain.