Iron-gall nut ink
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Iron-gall nut ink was the standard writing and drawing ink for Europe, from about the 12th century to the 19th century, and remained in use well into the 20th century.
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Preparation and use
The ink was prepared by adding some green vitriol (ferrous sulfate, Fe2SO4) to a solution of tannin (gallo-tannic acid). The latter was usually obtained from gall nuts (from oaks or other trees), hence the name.
A binder such as gum arabic was usually added to thicken the ink and make it flow properly from the pen. To extract the gallo-tannic acid, the gall nuts could be powdered and allowed stand in cold water for varying amounts of time, or boiled for several hours, or allowed to ferment for several weeks. The last two methods would hydrolyze the gallo-tannic acid into gallic acid, which yielded a deeper black color.
After filtering, the resulting pale-gray solution was used to write on paper, vellum (specially prepared calf hide) or parchment (various hides). A well-prepared ink would gradually darken to an intense purplish black. The resulting marks would adhere firmly to the vellum or parchement, and (unlike india ink or other formulas) could not be erased by rubbing or washing — only by actually scraping off a thin layer of the writing surface.
Chemistry
The gradual darkening of the ink was due to the oxidation of the iron ions from ferrous (Fe++) to ferric (Fe+++) state by atmospheric oxygen. (For that reason, the liquid ink had to be stored in a well-stoppered bottle, and would become unusable after a time.) The ferric ions then reacted with the tannin or some derived compound (possibly gallic acid or pyrogallol) to form a polymeric organometallic compound, which would make a strong chemical bond with the proteins of the hide.
While a very effective ink on vellum, the formula was less than ideal for paper, since the iron-tannin pigment would not make chemical bonds with the cellulose fibers. The ink still stuck firmly to the paper, but largely by mechanical bonding — namely the dried ink would penetrate the spaces between the fibers and, after drying would become entangled in them. Besides causing unsightly "ghost writing" on the obverse face of the paper, any excess of ferrous ions remaining by the ink, over years or decades, would create a rusty halo around the marks, and would ultimately cause the paper to disintegrate.
Demise
The permanence and water-resitance of the iron and gall-nut formula made it the standard writing ink in Europe for over 700 years. Its use only started to decline in the 20th century, when other water-proof formulas (better suited for writing on paper) became available. Nowadays, iron-gall nut ink is manufactured chiefly by artists enthusiastic about reviving old methods.
See also
External link
- http://www.knaw.nl/ecpa/ink/html/make.html - How to make iron gall ink