Iron Gall Ink

Part of Pigments and Paint

Making iron gall ink — the standard writing ink of Western civilization for over a thousand years.

Why This Matters

Iron gall ink was the dominant writing ink in Europe from the 5th century through the 19th century. The United States Constitution, the Magna Carta, and virtually every major Western document before the 20th century was written with some form of iron gall ink. There is a reason for this dominance: iron gall ink chemically bonds with paper and parchment fibers, making it virtually impossible to erase or wash away. It is the most permanent ink you can make from widely available natural materials.

For a rebuilding community, iron gall ink provides something carbon ink cannot: tamper-proof permanence. Legal documents, land records, medical protocols, and engineering specifications written in iron gall ink resist deliberate alteration. The ink literally becomes part of the paper through a chemical reaction that continues after writing.

The ingredients — oak galls (or any tannin-rich plant material), iron, and gum arabic — are available on every inhabited continent. Once you understand the underlying chemistry (tannin + iron = dark, permanent complex), you can adapt the recipe to whatever materials your environment provides.

The Chemistry

Iron gall ink works through a straightforward chemical reaction:

1. Tannic acid (from plant galls, bark, or other sources) reacts with ferrous sulfate (iron vitriol) to form ferrous tannate — a soluble, pale compound
2. Upon exposure to air, ferrous tannate oxidizes to ferric tannate — an insoluble, deep blue-black compound
3. This ferric tannate bonds chemically with cellulose fibers in paper and with collagen in parchment

This is why iron gall ink appears pale gray or brownish when first applied but darkens to black over hours to days. The ink is literally rusting onto the paper.

The Darkening Process

Fresh iron gall ink writes pale — sometimes nearly invisible. Do not add more iron to compensate. The ink darkens naturally as it oxidizes. Full color develops within 24-48 hours. Many historical recipes add a small amount of carbon ink to provide immediate visibility while the iron gall reaction completes.

Gathering Ingredients

Oak Galls

Oak galls (also called oak apples) are round growths on oak trees caused by wasp larvae. They are the richest natural source of tannic acid, containing 50-70% tannin by weight.

Identifying oak galls:

• Round or irregular growths, 1-4 cm diameter, found on oak twigs and leaves
• Green when fresh, turning brown and hard when the wasp has emerged
• Hard, dry galls with exit holes are ideal — they have the highest tannin concentration
• Collect in autumn for the best quality

Tannin alternatives if oak galls are unavailable:

Source	Tannin Content	Processing
Oak bark	Moderate	Boil 4-6 hours, reduce
Pomegranate rind	High	Dry, crush, boil 2 hours
Sumac berries	Moderate	Boil 2-3 hours
Tea leaves (strong brew)	Moderate	Steep in hot water
Chestnut bark	High	Boil 3-4 hours
Acacia bark	Moderate-high	Boil 4-6 hours

Iron Source (Ferrous Sulfate)

Ferrous sulfate — historically called “copperas” or “green vitriol” — is the iron compound needed. You can obtain it several ways:

1. Vinegar method: Soak iron nails, filings, or scrap iron in vinegar (acetic acid) for 2-4 weeks. The liquid turns yellow-brown as iron dissolves. Strain and use this iron acetate solution — it reacts with tannin similarly to ferrous sulfate
2. Sulfuric acid method: If sulfuric acid is available (from vitriol production), dissolve iron in dilute acid to produce ferrous sulfate directly
3. Natural deposits: Ferrous sulfate occurs naturally as the mineral melanterite near pyrite deposits. Dissolve in water and filter
4. Rust water: Rusty iron soaked in rainwater provides a weak iron solution. Functional but produces paler ink

Gum Arabic

Gum arabic comes from acacia trees — it is the dried sap that oozes from bark wounds. If acacia trees are not available, substitute:

• Cherry tree gum
• Plum tree gum
• Peach tree gum
• Hide glue (weaker substitute)

The Classic Recipe

This recipe produces approximately 250 ml of high-quality writing ink:

Ingredients

• 30 grams crushed oak galls (about 8-10 galls)
• 15 grams ferrous sulfate (or 100 ml iron-vinegar solution)
• 10 grams gum arabic
• 250 ml rainwater or clean water

Process

1. Crush the galls: Break oak galls into small pieces using a mortar and pestle. The pieces should be roughly pea-sized or smaller

2. Extract tannin: Place crushed galls in a ceramic or glass jar. Add 250 ml of water. Cover and let soak for 3-7 days, stirring daily. Alternatively, simmer gently for 2 hours (faster but produces slightly lower quality ink). The liquid should turn dark brown

3. Strain: Filter through fine cloth, squeezing the gall residue to extract all liquid. Discard the solids

4. Dissolve gum arabic: In a separate container, dissolve 10 grams of gum arabic in 2-3 tablespoons of warm water. Stir until fully dissolved — this may take an hour

5. Add iron: Dissolve ferrous sulfate in a small amount of warm water. Add to the tannin extract slowly, stirring constantly. The mixture will immediately darken

6. Add gum: Stir in the dissolved gum arabic. This gives the ink body and helps it adhere to the writing surface

7. Age: Let the ink rest in a covered container for 24-48 hours. Sediment will settle; this is normal. Decant the clear ink into a clean container

Iron-to-Tannin Ratio

Too much iron relative to tannin produces ink that is corrosive to paper — the excess iron sulfate forms sulfuric acid over time, eating through the fibers. This is why many historical documents have holes where the ink was. Use the ratio above, or err on the side of more tannin, less iron.

Adjustments and Variations

Immediate-Visibility Ink

Because iron gall ink writes pale initially, add visibility:

1. Grind a small amount of lamp black (soot) very finely
2. Add 1/2 teaspoon of soot to the finished ink
3. Stir thoroughly — the carbon provides immediate black color while the iron gall reaction develops underneath

Extra-Permanent Ink

For documents that must last centuries:

• Double the gall-soaking time (14 days instead of 7)
• Use slightly less iron than the standard recipe
• Apply to high-quality, acid-free paper or parchment
• Lower iron content reduces long-term acid damage while tannin provides permanence

Quick Iron Gall Ink

When you need ink today and cannot wait for galls to soak:

1. Boil crushed oak bark (or strong black tea) for 2 hours
2. Strain and reduce to one-quarter volume
3. Add iron vinegar solution while hot
4. Add dissolved gum arabic
5. Use immediately — quality is lower but functional

Working with Iron Gall Ink

Writing Properties

Iron gall ink flows differently from carbon ink:

• Thinner consistency: It penetrates paper fibers rather than sitting on the surface
• Slower drying: Takes 30-60 seconds to dry enough to handle; do not blot too soon
• Color shift: Writes gray-brown, darkens to blue-black over 24-48 hours
• Pen interaction: Works excellently with quill pens; can corrode metal nibs over time due to acidity

Pen Maintenance

The acidity of iron gall ink will damage metal pen nibs if not cleaned promptly:

• Rinse metal nibs in clean water after each use
• Wipe dry immediately
• Quill and reed pens are not affected by the acid
• Never leave iron gall ink in a metal container

Paper Compatibility

Iron gall ink works best on:

• Parchment/vellum: Ideal — the ink bonds with collagen, extremely permanent
• Rag paper: Excellent — high cellulose content provides good bonding
• Wood-pulp paper: Acceptable — the acid in the ink accelerates yellowing of acidic paper
• Sized paper: Paper treated with gelatin or alum sizing resists feathering (spreading)

Troubleshooting

Problem	Cause	Solution
Ink is too pale	Insufficient tannin	Soak galls longer; use more galls
Ink corrodes paper	Excess iron	Reduce iron; increase tannin
Ink flows poorly	Too thick	Add water; add more gum arabic
Ink feathers/spreads	Paper too absorbent	Size paper with gelatin; use less water in ink
Ink develops mold	Bacterial contamination	Add a few drops of vinegar; store sealed
Sediment forms	Normal iron tannate precipitation	Stir or decant; does not affect quality
Color stays brown, won’t blacken	Insufficient iron or wrong iron compound	Ensure iron source is dissolved; add more iron solution

Storage

Iron gall ink keeps well when stored properly:

• Use glass, ceramic, or wooden containers — never metal
• Keep sealed to prevent evaporation and contamination
• Sediment formation is normal — stir gently before use
• Shelf life: 6-12 months in sealed containers
• If the ink thickens from evaporation, add small amounts of water and stir

Ink Concentrate

Make a concentrated batch and dilute as needed. Concentrated iron gall ink (double-strength tannin extraction) stores better and longer than dilute ink. Add water at the point of use to achieve desired writing consistency.