A few years ago I went to a tiny but excellent exhibition all about ink at University College London, where a video was showing about how to make ink from oak galls. It’s been in the back of my mind ever since, so when I found myself camping under a line of oaks on the Gower in south Wales last week with oak galls dotted all over the grass, it seemed as if the time had come to give it a try. (oak galls – or oak apples – are little hard balls made when a parasitic wasp larva injects certain chemicals into developing leaf buds on the oak tree).

A little bit of research on the internet showed the key ingredients of this ancient ink (first known recipe by Pliny the Younger) are oak galls and iron, with gum arabic as a binder. The dark colour is created by a chemical reaction between the tannic acid in the galls and the iron sulphate. There’s a very informative website here. There are all sorts of minor variations, so I decided to create my own hybrid method, and here’s how it went:

Firstly, I put all the oak galls in a plastic bag and used a hammer to break them up. Then I ground up some out-of-date iron tablets I found in the cupboard, and threw in some old chunks of iron I found on Chiswick Eyot last week when learning about fish for Thames 21 (but that’s another story…). I put it all in an iron pot with some rainwater, and set some heat under it on the stove. Amazingly, it was only a couple of minutes before this orange soup turned a proper inky black. I boiled it all for a few more minutes, then strained it through an old tea towel. Finally I added the gum arabic, which gave the mixture a nice viscosity. In all I made half a pint of ink, which has a good dark brown colour – and once you’ve put it on paper, it continues to darken for a few hours. (the labels on the bottles are written with the ink)

It’s been a very interesting experience – much easier than I thought it would be to get a good result, and definitely something I would do again. I don’t know how long the ink will last, but I’m certainly going to start using it for drawing right away. Big thanks to Humphrey (age 4) for collecting all the galls for me!