Identification
Large tree with distinctive lobed leaves. Also, commonly appears in hedgerows. The two varieties of oak that are native to the UK can be distinguished their acorns.
The fruit, acorns, appear in mast years, occurring every 3-10 years.
Sessile oak
Quercus petraea. aka Cornish, Welsh, or Irish oak
Acorn has: bumpy cap, short stem
Pedunculate oak
Quercus robur. aka English oak.
Acorn has: bumpy cap, long stem
Hairy oak
A third species is also needed for the marble galls that we use in our practice. This was imported to the UK in 1735: the hairy oak.
Quercus cerris. aka Turkey or Austrian oak
Acorn has: hairy cap, short stem
These three oaks are critical for the development of marble oak galls, which are used to make the ink used to write the Magna Carta and the Book of Kells. You'll find the marble gall on either the Sessile or Pedunculate oak; however, you'll only find them if there is also a Hairy oak nearby.
Botany
Oaks will grow for more than a thousand years, and support hundreds of other species; several are completely dependent on the oak. These include the purple hairstreak butterfly and some gall wasps.
Part of the plant to use
Galls, acorn caps, bark (windfall only)
In our practice, we use marble galls, which are the easiest to find on Dartmoor. There are many other types of galls found on oak trees, which might be more common where you are.
The marble gall is approximately 2cm in diameter and is safe to use after a 2mm hole appears. This is the exit hole from the enclosed (non-stinging!) wasp.
The wasp, which is non-stinging and completely benign, that forms the galls uses both trees in its reproductive cycle. The Hairy oak were imported to the UK in 1735 as a garden tree. The wasps that make the marble galls (Andricus kollari) were imported to the southwest of England in 1835 -- specifically to make galls to support the textile dyeing industry! Before the arrival of Andricus kollari the galls used to make ink were either imported, or made from oak apples (wasp: Biorhiza pallida).
Lore
The oak king is that of summer, sunlight and growth. The oak is a tree of rebirth and the renewed cycle of life – experiencing a second growth of leaves in late summer. It is said oak enables us to focus on time and memory. It helps us manifest goals, perhaps thanks to its own longevity.
Ink Colour
Ochre: unmodified
Reddish brown: cooked in soda
Greys and blacks: + iron II sulphate
Reddish-orange: + baking soda
White “stars”: + citric acid
Making iron gall ink
A full recipe for making iron gall ink is also available.
Want to learn more?
We cover oak gall ink in-depth in session two of our botanical ink course, Galls to Nettles webinar series. The live sessions are over, but you can still buy the recordings (which come with comprehensive handouts, too). If you prefer print: Foraging for Colour includes an ink-making recipe for iron gall ink.