Iron Gall Ink

Part of Writing & Record Keeping

How to produce the most durable writing ink in history using oak galls, iron, and water.

Why This Matters

When you need records to last decades or centuries, not just years, the ink you write with matters as much as what you write on. Charcoal suspensions wash off, berry-juice inks fade to nothing in a season, and soot pigments sit on top of the surface where they can be rubbed away. Iron gall ink is chemically different: it reacts with the writing surface and bonds permanently into the fibers of parchment or paper, making it genuinely archival.

This ink was the dominant writing medium in Europe and the Islamic world for over a thousand years—from roughly the 5th century through the 19th. Every major document of Western civilization, from Magna Carta to the works of Leonardo da Vinci to Bach’s manuscripts, was written in iron gall ink. When you can produce it, you have access to a technology of extraordinary proven durability.

The ingredients are remarkably accessible. Oak galls—the round, hard growths that oak trees produce in response to wasp larvae—are found wherever oaks grow. Iron comes from rusty nails, iron filings, or any corroding ferrous metal. Gum arabic, the binder, can be substituted with other plant gums. This makes iron gall ink one of the most achievable archival writing materials for a post-collapse community.

Understanding the Chemistry

Iron gall ink works through a two-stage chemical reaction. When you understand what is happening, you can troubleshoot problems and optimize your process.

Stage 1 — Gallic acid extraction: Oak galls (and other plant material high in tannins) contain tannic and gallic acid. Soaking or boiling the galls in water extracts these acids into solution. The liquid is initially pale yellow-brown and looks disappointing.

Stage 2 — Iron reaction: When iron (as ferrous sulfate, or from dissolving iron in an acidic solution) is added to the gallic acid solution, ferrous gallate forms. This compound is initially light in color, but on exposure to air it oxidizes to ferric gallate—a dense, blue-black compound. This is your ink.

The gum arabic or plant gum you add serves as a binder and viscosity agent, keeping the ink from spreading too freely on the writing surface and making it flow consistently from the pen.

Why it darkens after writing

Freshly written iron gall ink often appears brownish or even grey. It darkens to deep black over minutes to hours as the ferrous gallate oxidizes in air. This is normal and expected. Very old manuscripts appear brown because continued oxidation over centuries eventually degrades the ferric gallate.

Sourcing and Preparing Materials

Oak Galls

Look for spherical, hard growths on oak branches, typically 1–3 cm in diameter. These are caused by gall wasps (Cynips species and relatives). The best galls for ink have a high tannin content—this correlates with denser, harder galls, often with a slightly rough surface texture.

• Collect in autumn when galls are fully developed and hardening
• Uninfested (empty) galls have higher tannin content than those still containing larvae
• Dry galls keep indefinitely; fresh galls can also be used immediately
• Other high-tannin sources work as substitutes: oak bark, pomegranate rind, sumac leaves, tea (strong), walnut husks

Gall preparation:

1. Crush or coarsely grind dried galls using a stone mortar
2. Soak in cold water for 24–48 hours, or boil for 30–60 minutes
3. Strain out all solid matter through cloth
4. The resulting liquid should be dark amber to brown

Iron Source

The traditional source is ferrous sulfate (green vitriol, copperas), a naturally occurring mineral. But you can make a functional substitute:

Rusty nail solution:

1. Place iron nails, iron filings, or any rusty iron scraps in a small vessel
2. Cover with a weak acid solution—diluted vinegar works well
3. Allow to dissolve for several days, stirring occasionally
4. Strain out undissolved material
5. The resulting greenish solution contains iron ions suitable for ink-making

The iron concentration doesn’t need to be precise. More iron produces a faster-darkening, denser ink; too much can make the ink corrosive and eventually damage parchment (this is the “iron gall deterioration” problem seen in old manuscripts).

Gum Binder

Gum arabic (from acacia trees) is traditional. Alternatives that work:

• Cherry tree gum (scrape from wounds on cherry or plum trees)
• Gum from other stone-fruit trees (peach, apricot)
• Weak flour-and-water solution (less ideal, can promote mold)
• Thin hide glue (very thin—just enough to add slight viscosity)

Dissolve the gum in warm water to make a moderately thick solution, then strain.

The Basic Recipe

This recipe produces approximately 200 ml of usable ink—enough to fill several small inkwells and write thousands of words.

Ingredient	Quantity	Notes
Oak gall extract	150 ml	Dark amber solution
Iron solution	50 ml	From rusty nails in vinegar, or ferrous sulfate
Gum solution	30 ml	1 part gum to 5 parts water

Method:

1. Combine the oak gall extract and iron solution in a clean vessel
2. Stir thoroughly—the mixture will darken almost immediately
3. Add the gum solution and stir again
4. Allow to stand for several hours, stirring occasionally
5. Strain through fine cloth to remove any sediment
6. Transfer to a sealed container

The ink improves with aging. Many historical recipes recommend allowing it to sit for weeks before use, stirring daily.

Testing your ink:

• Dip a reed or quill and make test strokes on scrap parchment or paper
• The ink should flow smoothly without beading up or spreading excessively
• It will look brownish-grey when wet; leave a test mark to air and check that it darkens to black within 30 minutes
• If it doesn’t darken, add more iron solution
• If it flows poorly, thin with a small amount of water

Adjusting and Troubleshooting

Problem	Likely Cause	Fix
Ink too pale, doesn’t darken	Too little iron	Add more iron solution gradually
Ink corrodes parchment over time	Too much iron	Dilute with more gall extract
Ink spreads and bleeds	Too thin, or surface is unprepared	Add more gum; size your writing surface
Ink clogs pen	Too thick or too much gum	Dilute with a little water
Mold grows in stored ink	Organic contamination	Add a few drops of vinegar; use cleaner vessels
Ink fades quickly	Low gallic acid content	Use higher-quality galls or more concentrated extract

Storing and Long-Term Use

Store iron gall ink in a sealed container away from direct light. Clay pots with tight lids, sealed glass jars, or wooden ink boxes with fitted lids all work. The ink will last months to years if stored properly.

Evaporation: Iron gall ink thickens as it ages due to water evaporation. Add a small amount of water and stir to restore consistency.

Sediment: A dark sediment will settle over time. This is normal ferric gallate precipitate. Stir before use, or decant the clear upper portion for fine writing.

Reconstituting dry ink: If the ink dries completely in its container, it can often be reconstituted by adding water and stirring. This is a feature, not a bug—you can transport dried ink tablets and reconstitute them at the destination.

Variations and Enhancements

Adding color: The standard iron gall produces blue-black to brown-black. Historical scribes sometimes added supplemental colorants:

• Boil in an iron pot to increase blackness
• Add soot or lampblack for deeper black (produces iron gall-carbon hybrid)
• Logwood extract adds a rich dark tone

Waterproofing: Once dry, iron gall ink is reasonably water-resistant because it is chemically bonded to the writing surface. For extra protection on important documents, a very light coating of beeswax rubbed over dried text can help.

Carbon additive: Adding a small amount of soot (lampblack) creates a hybrid ink that is darker when freshly written and more visually impressive, while retaining the archival bonding of iron gall chemistry. This was common in professional medieval scriptoria.

Teaching and Standardizing Production

When iron gall ink becomes a community resource, standardization matters. Develop a simple test:

1. Color test: Fresh ink should darken within 30 minutes on parchment
2. Flow test: Should flow from a reed pen at normal writing pressure without dripping or clogging
3. Permanence test: A mark made on a scrap, dried thoroughly, then wetted and rubbed—should not smear

Document your best recipe in standard proportions so that anyone trained in the process can reproduce it. Record the source of your galls (different oak species and different gall types vary in tannin content), your iron source, and any adjustments made. This recipe documentation is itself a piece of institutional knowledge worth preserving alongside the ink production capacity it describes.