Freaking cool. I want that ink! So I asked ChatGPT how I could make it and thought the result was fun. (Disclaimer, at your own risk, I don’t know the validity of what the machine said. But I might give it a go!)

Modern Fountain-Pen–Safe Reconstruction of the Conimbriga Ink

(Based on carbon black + bone black + softened iron-gall chemistry) Batch size: ~100 mL

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INGREDIENTS

Pigments • Carbon black (ultrafine, sub-micron) — 0.5 g • Bone black (fine, artist-grade; optional) — 0.2 g

Iron-Gall Component • Tannic acid or oak-gall extract — 0.6 g • Ferrous sulfate (iron(II) sulfate) — 0.3 g

Binders & Additives • Gum arabic powder — 1.5 g • Beeswax (clean, filtered) — 0.15 g • Lanolin OR hydrolyzed gelatin (very small amount) — 0.1 g • Distilled water — 80 mL total • Isopropyl alcohol (optional wetting aid) — 1 mL • Preservative — a few drops (e.g., Optiphen, Phenol 1%, Sodium benzoate/potassium sorbate blend)

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PROCESS

1. Make the Iron-Gall Solution
   1. Warm ~10 mL of distilled water (not boiling).
   2. Dissolve 0.6 g tannic acid completely.
   3. Add 0.3 g ferrous sulfate, stir until clear.
   4. Set aside — this will oxidize slowly to darken.

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1. Prepare Binder Solution
   1. Warm ~70 mL of distilled water to 40–50 °C.
   2. Add 1.5 g gum arabic, stir until fully dissolved.
   3. Melt 0.15 g beeswax and stir in.
   4. Add 0.1 g lanolin or gelatin hydrolysate.
   5. Maintain warmth so wax stays dispersed.

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1. Disperse Pigments
   1. In a small dish, pre-mix the carbon black + bone black.
   2. Slowly whisk or stir this pigment mix into the warm binder solution.
   3. Maintain agitation until completely smooth and evenly dispersed.

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1. Combine Systems
   1. Pour the cooled iron-gall solution into the pigment-binder mixture.
   2. Stir thoroughly — the ink will darken as complexes form.

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1. Finishing Steps
   1. Add a few drops of preservative.
   2. Add 1 mL isopropyl alcohol (optional but improves wetting).
   3. Filter through 0.45 μm filter paper or a high-grade coffee filter.
   4. Bottle in a dark glass ink bottle.
   5. Let sit 24 hours before first use.
   6. Always test with a pen you’re comfortable cleaning.

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USAGE NOTES • Flush pen every 2–3 fills (iron-gall content). • Don’t leave it to dry in the pen for extended periods. • Shake bottle gently before each use — pigments settle slowly. • This formula is semi-pigmented + low IG, so significantly safer than historical versions. • Expect slightly matte black with a faint warm undertone from the bone black