copper ink

Ingredients

gall nuts, water, copper (II) sulphate

Preparation Steps

Original Recipe Text

15 g of gall nuts were cooked in 30 g of water for ten minutes after boiling. 0.3 g of pure copper (II) sulphate was progressively added to the warm solution (p. 145).

Evidence

"I then progressively added pure copper (II) sulphate (0,3 g) to the still warm solution: it turned dark brown. I used it to write with a reed pen on handmade paper with no iron: as a result, the ink had a light brown colour [...] writing with a metallic pen, obtaining a very dark brown colour."

Remarks

The experiment demonstrates that copper (II) sulphate does not form a black complex with gallic acid. However, when used with a metallic (iron) pen, an ionic exchange occurs: iron ions from the pen replace the copper ions in the ink, forming a darker ferro-gallate complex. This explains why some historical 'vitriol' recipes (specifically those identifies as copper-based by al-Rāzī) might have still functioned (p. 145).