Hasfield Court Walled Garden, in Gloucestershire, has sent me a little bag of oak galls. I've used them in the past to pre-mordant plant fibres, but thought I'd use this bag to try some oak gall ink. Patricia Lovett of the British Museum explains that oak gall ink was used for centuries for recording important documents, because of its rich, dark colour, its indelibility and permanence. You can't get more expert than the British Museum, so I'm following her instructions.
A word first about oak galls, those little hard round growths found on the branches of oak trees. They're formed when the oak gall wasp (there are many different types) lays eggs in the tissues of the host tree. As they develop they produce chemicals that modify the growth of the plant to create the protective gall within which the new wasp grows. Small holes can be seen in the gall where the young wasp eventually emerges.
There are as many types of oak gall as there are oak gall wasp, and in the 1800's the Andricus kollari wasp was intentionally introduced from the Mediterranean to produce the 'marble' oak gall which is particularly rich in tannin. The oak gall I'm using is the 'knopper' oak gall, produced by the Andricus quercuscalicis wasp. Unlike the marble oak gall, which tends to remain on the branch, these fall to the ground in the autumn making them easier to find and gather. However, I do not know how tannin-rich they are, but we'll find out!
To coax the tannin from the galls it's necessary to crush them into little pieces, cover them in water and leave them to stand on a window sill for a few days. That's what I did today and I'll be hovering over the jar with interest, and hoping to see a gradual colour change as the tannin seeps into the water and turns it brown. To be continued ....!