Making & Testing Iron Gall Ink

By Sakura Tohma

Recently we tried making iron gall inks!!

Iron gall ink is produced by the reaction of tannic acid extracted from galls, a type of growth on trees (especially oak), with ferrous sulphate (FeSO4).

This ink has been the most common type in the Western world from the 9th century until the 20th century, but a lot of historical manuscripts written with this ink suffered terrible damage. Poor quality ink fades, and/or causes the paper around the ink to darken and become brittle. This can lead to the creation of fragments or complete loss of stability of the support.


- Gall: A growth caused by insects, usually a wrasp or fly, which lay eggs into young tissue in the tree. The larvae grow up in the gall, which has a higher quantity of gallotannic acid than the rest of the tree. The ink can be made with other sources of tannins as well, but this is one common source.

[caption id="attachment_4435" width="640"]DSC_1375 Galls from an oak tree[/caption]

[caption id="attachment_4436" width="640"]DSC_1528 Galls collected by Abby Bainbridge from mystery tree in Portugal[/caption]

- Ferrous sulphate (FeSO4): A metallic salt that forms blue-green crystals. In ancient times, people used naturally-occurring melanterite (FeSO4・7H2O).

- Water

- Gum Arabic: Resin extracted from the acacia tree, a translucent amber colour. It works in the ink both as a binder and to modify its flow. It allows for better surface tension of the ink on the nib, and makes it easier to write more with each dip into the ink.

Our method of making iron gall ink

1. Break the galls into pieces.

There are some hollow spaces inside the galls. Maybe these were the insects' bedrooms?

The insides of the black gall were black, yellow in the yellowish one, and red in the reddish one.

I found an insect!! In most of the galls, exit holes mean the insect has already left-this one was still solid so we thought there would be a chance. Can you see it?

I tried to magnify him with a macro lens. He is a little broken up, but still has one leg and wings.

2. Add the water to the ground galls.

Gallotannnic acid is extracted by heating or just soaking for a few days. Gallotannin is hydrolysed to gallic acid and glucose.

The liquid turned dark brown in 3 minutes.

3. Filter the gall and water mixture.

The ink was filtered twice through filter paper in a funnel.

4. Add the ferrous sulphate

After adding ferrous sulphate to the solution, the colour turned from brown to black immediately! It is because gallic acid reacts with ferrous cations; together they make ferrous gallate, which is black in colour.

gallic acid + ferrous cation -> ferrous gallate

5. Add the gum arabic.

Crushed gum arabic is put into the solution. When it dissolves, the ink is completed!

I tried writing on paper with the new ink. When the ink was applied, it was translucent grayish brown (bottom squiggle in the photo above). Over a few seconds, the colour gradually turned deep black (top squiggle)!

This is the reaction of ferrous gallate and oxygen from the air. The black of iron gall ink comes from ferric pyrogallate (the Fe2+ is oxidized to Fe3+)!

ferrous gallate + oxygen -> ferric pyrogallate + H2O

Various recipes have existed since Middle Ages. This time, I used following recipe:

- 5 galls 5g

- water 75ml

- ferrous sulphate 1g

- gum arabic 1g

It was quite thick. One of us is experimenting with other recipe, using beer and vinegar instead of water. I am looking forward to her ink!

A few days later--

We tested our own inks with Fe(II) test paper, which is filter paper impregnated with bathophenanthroleine.

In paper conservation, if iron gall ink contains unbound ferrous ions, water cannot be used for treatments. It means that the damaged paper cannot be repaired with wheat starch paste and Japanese paper, because Fe(II) causes paper degradation and it is water soluble. If water drops on the paper, it can cause the ferrous ions to spread and the paper degradation might spread as well. When there is too much ferrous sulphate in recipe, surplus ferrous ions remains in the ink and they cause paper degradation.It was easy for this to happen because quantities weren't normally measured very carefully and the ingredients were cheap. Many historic inks contain too much Fe(II).

Ferrous= Fe(II)= Fe2+

Ferric= Fe(III) = Fe3+

Colorimetric method using Fe(II) test paper

This paper can show to what extent ferrous ions are in the paper.

If the paper has ferrous ions, the colour of the paper turns pink. The intensity of the pink shows the amount of ferrous ions.

Bathophenanthroline has been soaked into the test paper (we bought it ready-made but you can make your own). Bathophenanthroline reacts with ferrous ions to form a pink complex but doesn't react with ferric.


A small piece of the test paper is dipped in deionised water, and put onto the ink to be tested for about 30 seconds. After a while, if the test paper turns pink, the test is positive for ferrous ions.

* The test paper should not be touched by bare hands and it should be handled with plastic or stainless steel tweezers, to avoid contamination & false positives.

We tried using the test to a textblock written in iron gall ink with significant water and mould damage at the fore-edge. We would like to repair it with wheat starch paste, for strong repairs, but not if the ink is unstable.

It didn't change! Starch paste can be applied. Good!!

How is our ink?

Then we tried it on the ink we made above. We dropped some ink onto paper then tested the paper. Wow! Nice pink! We made bad inks. We should try again after the ink has had time to oxidize, though, because it might not be as bad then.

In good recipes, all ferrous ions will react completely with gallic acid. Next time, I would like to find a good recipe!