Oak gall ink is a slow ink. It starts pale, writes grey-blue, and only later darkens to the near-black line we associate with old manuscripts. That slow change is not a flaw; it is the ink’s nature. Unlike carbon-based inks that sit on the surface, iron gall ink reacts with the paper itself, so the final mark is unusually tenacious.
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What Makes Oak Gall Ink Work
Oak galls are rounded growths that form on oak trees after a gall wasp lays its eggs. The tree builds a protective shell around the larvae, and that shell is rich in tannins. When an iron salt such as iron sulfate is added to a water extract of those galls, the tannins and iron combine to form a soluble blue-black pigment. As the liquid dries and is exposed to oxygen, it oxidizes into the darker iron tannate.
Gum arabic is the third essential ingredient. It is a natural gum that keeps the pigment in suspension and gives the ink a smooth, controlled flow from a nib. Too little gum makes thin, scratchy lines; too much makes a syrupy liquid that clogs the pen.
Many medieval and early modern manuscripts were written with an ink of this family. The darkest surviving lines still appear black because the pigment is embedded in the fibers rather than lying on top of them. The same reaction can also be hard on paper if the maker uses too much iron sulfate, which is why the proportions matter.
Materials
Before starting, gather:
- Dried oak galls
- Iron sulfate (also sold as copperas or ferrous sulfate)
- Gum arabic
- Distilled water
- A glass jar for steeping and mixing
- A fine cloth or paper coffee filter for straining
- A small bottle with a cork or lid for storage
Use dried galls. If you have collected fresh ones, spread them on a tray in a warm, airy place and let them dry before crushing. Iron sulfate can irritate the skin and eyes, so wear gloves, avoid raising dust, and keep the powder away from children.
A small non-reactive pan is useful if you choose the warm extraction method described below. Do not use an iron, steel, or aluminum pan or spoon.
How to Make Oak Gall Ink
1. Crush the oak galls
Place the dried galls in a strong cloth and break them with a hammer, rolling pin, or a clean stone. You want pieces about the size of a pea or smaller; a fine powder will make filtering difficult. Use 30 g for a first batch.
2. Steep the galls in water
Put the crushed galls into a glass jar and pour 300 ml of distilled water over them. Cover the jar with cloth and leave it at room temperature for 24 to 48 hours. The water will turn a warm tan. If you prefer a quicker extraction, warm the galls and water gently for 45 minutes without boiling, then let them cool before straining. A cold steep often makes a cleaner, less cloudy final ink.
3. Strain the tannin liquor
Pour the liquid through a fine cloth or filter. Collect the darkest liquid and discard the crushed galls. Do not force every last bit of pulp through the cloth, because tiny fibers will later clog a nib.
4. Add the iron sulfate
Weigh 12 g of iron sulfate and stir it slowly into the strained liquid. The mixture will immediately change color and begin to look like ink. Cover the jar loosely and let the liquid sit overnight. Oxygen is part of the reaction, so do not seal the jar completely.
5. Prepare and add the gum arabic
Dissolve 6 g of gum arabic in a small amount of hot distilled water, allow it to cool, and stir it into the ink. Add it gradually, because the ideal amount depends on the strength of your tannin extract and the nib you plan to use.
6. Let the ink rest, then bottle it
After a few days, the solution will settle. Decant the clearer liquid into a small bottle, leaving the sediment behind. Keep the bottle loosely closed, or open it from time to time, so the ink can continue to take up oxygen. Freshly made oak gall ink will write a pale blue-grey line; the dark color appears as the ink oxidizes. Test it on scrap paper and keep the test sheet for comparison after a week.
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Controlling Color and Flow
The ratio given above is a starting point, not a fixed rule. For a darker initial line, add iron sulfate in small amounts and wait a day before deciding. For a richer brown-black, steep the galls longer or add another small batch of crushed galls to the extraction. If the ink seems flat or grey after a week, a little more iron sulfate will push it darker.
Do not be tempted to pile on iron sulfate. Excess iron is what gives iron gall ink its reputation for eating through paper. The safest route is to keep the iron modest and rely on steady oxidation to deepen the color.
Flow is controlled almost entirely by gum arabic. If the ink skips or gathers at the top of the nib, add a drop of dissolved gum arabic to the bottle and shake gently. If the ink feels tacky, glossy, or hard to scrub out of a brush, you have added too much. Thinning with distilled water usually corrects it.
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Using the Ink for Drawing and Writing
Oak gall ink is best used with a dip pen, quill, or brush. Do not put it in a fountain pen unless your batch has been filtered extremely well and you are prepared to clean the pen thoroughly; home-made iron gall ink can clog and corrode pen mechanisms.
With a dip pen, expect to dip often. The ink will not flow as heavily as a manufactured carbon ink, and the nib needs a fresh charge to lay down a continuous line. Rinse the nib in clean water every few minutes to remove the tiny particles that gather at the slit. Dry it gently with a cloth.
When drawing, use the pale first stage to your advantage. You can lay down loose, light strokes, allow them to dry, and then build darker layers. The final value will be deeper than it appeared at first, so stop before the page looks overworked. An overnight rest will reveal the true tone.
Diluted washes are also useful. Keep a small jar of clear distilled water beside the ink. Dip a brush in the water, touch it to the ink, and work on a palette until the wash is the strength you want. These pale washes will not stay pale forever; they will darken with the same oxidation that darkens the stronger lines.
Troubleshooting
- Cloudy ink: Let the bottle sit for several days and pour off the clear upper layer.
- Skips and uneven lines: Add a little more dissolved gum arabic, or rinse the nib more often.
- Pale after a full week: Add a trace more iron sulfate, wait two days, and test again.
- Line spreads on paper: The mixture is too wet; add gum arabic and test on a less absorbent paper.
- Sediment in the bottle: Do not shake the bottle before filling a pen. Dip from the top, leaving the settled material below.
Why Some Old Inks Endure
The permanence of iron gall ink is not simply a matter of age. In a well-made batch, the iron pigment becomes fixed inside the paper fibers, which makes it more resistant to light than many dyes. That is why countless old manuscripts still contain dark, legible strokes. In poorly made batches, excess iron sulfate left a residue of acid that weakened the paper over time. The remedy is to respect the old recipe: enough gall tannin, a modest amount of iron, and gum arabic to keep the ink even.
Made in small batches, oak gall ink carries the character of its ingredients. The first stroke seems tentative, then oxidizes into a dark and settled line. That waiting period is part of the craft.