Oak Gall Ink
Over 30 species of parasitic Oak Gall Wasps can infect our native oak trees (both English and Sessile). These wasps lay their eggs in various parts of the tree and the tree responds by producing abnormal growth around the egg and developing larvae which is the gall. Depending on the species of wasp, the galls can vary from small disks to large ridged woody structures, and some wasp species have two parts to their life cycle and produce different galls in different parts of the tree depending on the stage of their life cycle.
Perhaps the Oak Galls most familiar to many people are two spherical shaped galls that are found on the twigs of oaks; the large (up to 5cm) Oak Apple Gall by the wasp Biorhiza pallida and the smaller (up to 2cm) Oak Nut or Oak Marble Gall produced by Andricus kollari which are confusingly also sometimes called Oak Apples
Both these galls (and other galls) have a high tannin (gallotannin and gallic acid) content and it is this feature which has led to their use in the manufacture of ink. Historically the tannins where extracted, often by fermentation and then reacted with iron sulphate to form iron tannates. These are generally Iron (II) salts and are grey in colour but with exposure to atmospheric oxygen become oxidised to Iron (III) salts which are dark purplish black. Gum arabic was often added as a binder. Its use can be traced back at least to Roman times and was used right up until the 20th century. Documents such as the Magna Carta and the American Declaration of Independence where written with oak gall ink.
To make it yourself is easy, there are different ways of doing it but this method is quite straight forward.
Firstly take some steel wool and place in a small container and cover with some vinegar (cheap malt vinegar is fine) or lemon juice and allow to sit for a few days to allow the iron to dissolve.
Take a couple of good handfuls of oak galls and break up into small pieces.
Place in a pan and cover with water. Bring to the boil and simmer for 20-30 minutes until you get a nice dark brown solution as all the tannins are released.
Strain out all the bits of oak gall and allow to cool.
It is simply a case of then mixing together the two solutions.