When you’re out enjoying the Autumn leaves, you may find some of these curious growths among the boughs of the oak trees. Not acorns, not leaf buds, nor a fungus, these rounded, sometimes spiked woody additions are oak galls. They form when a type of gall wasp lays an egg in a fresh bud. The tree responds by sending tannic acid to the area and growing a chamber around the egg to protect itself from infection. The egg, in turn gets a little nursery to grow in until the young wasp is born and gnaws a channel out of the gall.
It's the concentration of tannic acid in the gall that has made them a useful resource for making ink. When steeped in water, the galls release a rich brown colour. When mixed with iron sulphate (or vitriol as used to be known), the tannic acid reacts to create a deep blue black. With some gum Arabic, this mixture serves as an excellent ink. Iron gall ink has been used as a medium for drawing and writing for many centuries, though how far back the practice goes has not been established. It has been prized throughout the ages as an indelible ink, as it’s not prone to fading or washing away. It does however tend to change to a more brown colour over time due to the iron corroding. Recipes for iron gall ink are numerous and yield a variety of results. In some cases, the combination of iron and acid can cause the ink to corrode right through paper and parchment.
Here a few drawings that may have been drawn using iron gall ink:
Jen Bowens is an Irish Paper Conservator working at Amgueddfa Cymru as part of the Celf project. Jen specialises in the conservation of works of art on paper, but also works with archival material and books. Outside of work, Jen enjoys making art, hiking and birdwatching.
