Iron gall ink is a black ink made from oak galls, iron salts, and gum Arabic. Iron gall ink has been in use for thousands of years. It is considered permanent, and has been used for legal documents until recently. Oak galls are wasp incubation pods found on oak trees.

Iron gall ink is also known as oak gall ink; however, technically you should include the word “iron” if it contains iron.  (I use both interchangeably, but I'm trying to be better.)

History of Iron Gall Ink

In use for more than 2000 years. Generally agreed to be the “standard” ink for scribes and authors from the Middle Ages until at least the 18th century. Earliest known written recipe is from Pliny the Elder (1st century CE/AD). There are many famous recipes for iron gall ink, including one used by Jane Austen, and the USA government standard recipe from 1935.

About oak galls

Galls are the protective incubation pod formed by the oak tree in response to being injected with a wasp egg. There are more than 60 types of wasps that use oak for their life cycle. Different wasps use different parts of the tree to lay their eggs (e.g., root, bud, leaf, branch, acorn, catkin). Not all oak galls have the same concentration of tannic and gallic acids. [source]

How the ink works

The oak galls contain a mixture of tannic and gallic acids*. These chemical compounds are related (many gallics are included in a tannic). There are differing concentrations of the chemicals based on the type of gall (which is based on the type of wasp). When mixed with iron, the acids form new chemical compounds. These chemical compounds are black, bond with paper, and are (relatively) waterproof after a few days.

*it’s more complicated than this, but this is a good starting point

Basic recipe

Quick Start

Collection

• Find your local oak trees.
• This is easier when the leaves are on!
• Look for galls. Collect the ones with exit holes.
• (If you don’t live near appropriate oak trees, it is possible to buy galls. Search for local natural dye suppliers in your area.)

Make ink

• Crush the galls.
• Simmer (or long soak) the galls.
• Filter into a storage jar.
• Add the tiniest bit of iron II sulphate (or rusty nail water).
• Add gum Arabic.

An exact recipe is impossible because the amount of gallotannins varies in the natural ingredients. Be okay with “ish”, and be okay with variation between batches.

Find (or buy) galls and/or acorn caps

For us, it takes about a year of searching Dartmoor to find enough galls to make a batch of ink. A few dozen galls will make about 250ml of ink.

Acorn caps can also be used, but they aren’t as potent. Expect grey instead of black ink. 2025 is a mast (abundance) year for acorns. If you live in an urban area and see the acorns are getting crushed, scoop them up and use them for ink-making! In non-mast years: harvest the caps, but leave the acorns for the critters to eat.

Crush and cook the galls

Crush the galls. The finer the better. Cover the crushed galls in water. Add that much water again. Bring to a boil and then reduce heat. 75C is ideal, but not critical to success. Simmer until your test strip of paper is “dark enough”. 15-20 minutes is usually just long enough. You now have oak gall liquor. Cooking breaks down the cell walls, and releases the important chemical compounds that we’ll need.

Alternatively, soak

Rinse debris off the galls. Bash them about a bit so the pieces are a few mm in size. Cover with water. (Some historical recipes used wine or vinegar or beer to lower the pH, potentially changing which gallotannins are extracted.) Leave for 6-10 days, stirring occasionally. Scoop any mould off, and proceed with the next step. The long soak allows the chemicals we need to leach out of the cells over time.

Add iron

Strain out the crushed oak galls. Now you have oak gall “liquor”. For each 250ml of oak gall liquor, add 1/8th tsp of iron II sulphate. The liquid will change colour, usually darker brown but can vary. This is not the final colour. Paint a little onto a test strip and wait. As the ink reacts with oxygen, it will continue to darken. Usually, within a minute or two, it will be nearly black. Although you may be tempted to add more iron, resist. Adding too much can burn the paper over time.

Add gum Arabic

For each 100ml of iron gall water, add 10ml of gum Arabic.

Gum Arabic helps:

• Keep the pigment suspended
• Makes the ink flow properly from a dip pen
• Helps stabilize black chemical compounds

Without gum arabic, you have a mixture that will separate and is difficult to write with. With gum arabic, you have a stable, workable ink. You may need to adjust the amount of gum Arabic to suit your purposes.

Which gum Arabic?

For oak gall ink: any food-grade gum Arabic is fine. You don’t need to spend extra on artist grade (liquid). If you buy unprocessed lumps, you’ll need to cook in water to dissolve it. If you’re feeling outrageous, just pop a couple of lumps into the iron gall liquid. It will eventually dissolve. If you buy ground gum Arabic, you will need to add water. If you’re making your own gum Arabic liquid: it should be “about” the consistency of double cream. It will not be as clear as artist grade. For iron gall ink, this doesn’t matter.

We have purchased our gum Arabic from eBay. If you live in a city, check your local dry food / bulk food shop. They may stock it.

Substitutions for iron II sulphate

If you don’t have iron II sulphate, you can make a rust plant using iron nails/pipes/horseshoes/steel wool (etc), vinegar, and patience. This is less effective, and not traditional, but also free. You can also use crushed up iron tablets. This is very expensive, though.

Troubleshooting

If your ink is black when wet, but green/brown when dry, you are probably adding too much iron. The extra iron is free to interact with other chemical compounds, and make other colours. Ooops. Thanks to Lucy Mayes for this tip!