Iron-gall nut ink

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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.

1 Preparation and use
2 Chemistry
3 Demise
4 Warning
5 See also
6 External link

[edit] Preparation and use

The ink was generally prepared by adding some green vitriol (ferrous sulfate, Fe S O₄) 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.

One must be careful when dealing with some, unfortunately, close terms mistakenly used as if interchangeable: Most literature describes a whole group of chemicals, related in terms of *where* they are found, but not necesserally in structure as "Tannins" - Use the wrong one and either you will get no ink OR your leather will not tan...

In the case of ink, we want to extract gallo-tannic acid, and hydrolize it to form gallic acid, then react that with FeSO4. During the initial extraction, a rush of tannic acid will probably pour from the galls, turning the accumulating liquor reddish brown and filling the room with the scent of tea.

Would that there were an easy way to separate out this waste product, which can block the constructive portion of the reaction, and would be much more useful, extracted, in tanning a nice cow hide or giving a tea enthusiast the shock of his/her life.

Wait - let mold, mostly pennicillia, grow, 10 days or so, hydrolizing the gallo-tannic acid to plain gallic acid. Strain the crushed galls through muslin and squeeze out every drop of the liquor, tearing at the cork-like fiber to make sure all is extracted.

Then add the FeSO4, slowly, and you may, by waiting and stirring, produce fine ink with a lower-than-normal acid content.

While daily adjusting the quantity of FeSO4 and allowing the ink to mature, crush up a quarter of a large tear of gum arabic per oz of ink with a hammer or mortar, or mix the powdered form now available from food producers with a little hot water and allow to sit for a day or two before pouring the concentrated slime into the ink pot.

The binder such as gum arabic was usually added to thicken the ink and make it flow properly from the pen.

Alternatives: To extract the gallo-tannic acid, the gall nuts could be crushed and allowed to 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.

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 Jewish ritual Torah scrolls - if a letter is ever found cracked, common with a vellum document rolled and rerolled daily, it must be removed in its entiraty 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.

[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 nut ink is manufactured chiefly by artists enthusiastic about reviving old methods.

[edit] Warning

Iron-gallnut 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.