Oak Gall Ink, sometimes called Iron Gall ink, has been the most common form of ink used for thousands of years, with many important documents and manuscripts written with it. The oldest and most complete Bible known to exist was written using oak gall ink, and Di Vinci painted with it. This is due to it being inexpensive, easy to make and light stable; meaning it is permanent and will not fade over time. The ink is a rich dark brown or black ink made from the galls of oak trees and an iron solution.

Oak galls are a hard circle that forms on an oak tree when the parasitic gall wasp lays her eggs on the tree and the tree responds by forming a barrier around the eggs effectively cocooning them. When the larvae mature, they burrow out of the gall via a tiny hole and the empty gall remains. If you find galls that do not have any holes, then leave them in place until the wasp has left.

The oak tree is high in tannins, with the galls being extremely high in tannins (gallotannic acid) which forms the basis of the ink. Tannins have been used to make inks, dyes, mordants and to ‘tan’ leather. The tannins need to be extracted from the oak galls by soaking in rain or distilled water.

Roughly smash the galls with a hammer (they are very hard) to aid the leaching process, and cover with rain or distilled water. The gall water can be left on a windowsill for a few weeks or if can be boiled in a pot on the stove to speed up the process.

Strain the brown liquid (Gallotanic acid) from the crushed oak galls, reusing the galls as many times as colour can still be extracted.

A gluelike binder needs to be added to the solution as that will enable the ink to adhere to the paper. A solution of Gum Arabic is normally used, which is the hardened sap of a few different tree species most notably the Acacia tree. It is an emulsifier, helping to keep the pigment suspended in the liquid, helps with the flow of the ink, will help to keep the marks and lines on paper clearer and sharper, and will thicken the solution up. It can be purchased in amber coloured lumps, in powder form or in a prepared solution. I use the powdered type and dissolve directly in the warmed tannic solution.

It can be used at this stage, however it will be still quite a pale brown and not permanent, therefore an iron solution needs to be added to darken the colour and to waterproof it.

In medieval times ferrous sulphate was also known as copperas or green vitriol ( note the potential confusion. Iron salts in the form of ferrous sulphate are green and copper salts are also green, however we are talking about iron and not copper). Ferrous sulphate can be purchased in the form of green salts, however you can make your own solution by taking some old iron nails and placing them in a jar, fully covering them with household vinegar and let sit for a few weeks.

Adding the iron solution (ferrous sulphate) to the oak gall solution ( gallotannic acid) will darken the ink immediately (ferrous tannate). The water soluble solution will penetrate the paper making it difficult to erase, yet when exposed to air, the solution becomes ferric tannate and the ink will darken even more with oxidation and is now no longer water soluble and therefore water proof.

A lot of old recipes call for wine, vinegar or beer instead of water. This would have a preservative effect on your ink making it last for longer, but it will also increase the acidity of the ink which would damage the paper. That said, a little vinegar (one single drop) is said to add gloss.

Several countries had set laws detailing the exact qualities that the ink had to adhere to, to ensure the permanence of legal documents due to the acidity of the ink and its ability to eat through the paper if not controlled.

Modern Recipe

Oak Galls 5g

Rain or distilled water 75ml

Gum Arabic 1g

Ferrous Sulphate 1g