Ancient Gall Ink

When reading books on textual criticism and palaeography, I have often noted references to "gall ink" or "ink made from nut galls" in sections dealing with the making of ancient manuscripts. "What in the world is a nut gall?" I'd briefly wonder and then continue on with my reading. I never really thought to look it up until recently when I was reading one of the new sections in the fourth edition of The Text of the New Testament by Bruce Metzger and Bart Ehrman and stumbled across the following interesting information:

An oak gall is a curious ball-like tumor, about the size of a small marble, that grows mainly on the leaves or twigs of oak trees. It is formed when the gall wasp lays its egg in the growing bud of the tree and a soft, pale green, apple-like sphere begins to form around the larva.

These "tumors", or "galls", contain tannic acid. They were ground and mixed with iron sulfate, gum arabic, and liquid (eg. rainwater, beer, or wine) to form an indelible black ink.

Though it is hard to determine when gall ink was first used, it is often mentioned that Pliny the Elder (23 -79 AD) recorded an experiment in which he noted the reaction of iron sulfate on a sheet of papyrus that had been soaked in tannic acid:

The fraud may also be detected by using a leaf of papyrus, which has been steeped in an infusion of nut-galls; for it becomes black immediately upon the genuine verdigris being applied.

Pliny the Elder, The Natural History, Book 34 Chapter 26

However, in spite of this observation by Pliny, it appears that iron gall ink was not in use until centuries later. Martianus Capella, of the 5th century, records a recipe for a writing ink described as "gallarum gummeosque commixtio". The use of iron gall ink eventually became popular and wide-spread due to the fact that it does not easily rub off or erase.

Iron gall ink turns light brown over time (as can be seen in this image of a fragment from Euclid's Elements of Geometry). The acidic properties of iron gall ink are corrosive and can destroy important historical documents as they age. The Ink Corrosion Website presents tons of interesting information on iron gall ink and on conservation efforts.

Here are a few other related links that might be of interest:

• Images of oak galls
  
• Iron Gall Ink (for those who enjoy the occasional chemical reaction diagram)
  
• Iron-Gall Ink, Indelible Ink, Encaustum
  
• Forty Centuries of Ink