Iron gall ink
From Wikipedia, the free encyclopedia
Iron gall ink (sometimes iron gall nut ink) is a purple-black ink made from iron salts and tannin from vegetable sources. It was the standard writing and drawing ink in Europe, from about the 12th century to the 19th century, and remained in use well into the 20th century.
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[edit] Preparation and use
The ink was generally prepared by adding some ferrous sulfate (FeSO4) to a solution of tannin (gallotannic acid). The latter was usually extracted from oak galls (also known as "oak apples"), or galls of other trees; hence the name. Fermentation or hydrolysis of the extract releases gallic acid, which yields a darker black ink. The fermented extract is combined with the ferrous sulfate and a binder such as gum arabic.
After filtering, the resulting pale-gray solution was used to write on paper or vellum. A well-prepared ink would gradually darken to an intense purplish black. The resulting marks would adhere firmly to the vellum or parchment, 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.
That it *can* be completely removed was sufficient to allow this ink, or a galloferric ink with added carbon black, (lamp black) to be used in making Torah scrolls - if a letter is ever found cracked, common with a vellum document rolled and rerolled daily, it must be removed in its entirety before it is redrawn for the scroll to remain ritually pure. This has apparently led to many a "red" Torah, where leaves of vellum have, over the years, faded to a still perfectly legible red, harbinger of future destruction[citation needed].
[edit] Chemistry
The gradual darkening of the ink was due to the oxidation of the iron ions from ferrous (Fe2+) to ferric (Fe3+) 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. The gallol would then make strong and permanent chemical bonds with the proteins of the hide, by the same chemical processes underlying tanning.
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.
[edit] Demise
The permanence and water-resistance 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 ink is manufactured chiefly by artists enthusiastic about reviving old methods.
[edit] Warning
Iron gall ink is not suitable for fountain pens as it will corrode them very quickly. Instead one should use modern surrogate formulas such as Montblanc blue-black, which has a very small amount of the ferro gallic compounds, or Rohrer & Klingner "Scabiosa" and "Salix" inks, both of which require the fountain pen to be flushed out regularly with water.
[edit] See also
[edit] External link
- How to make iron gall ink, at an ink corrosion website.
