Conserving a mould-damaged iron gall ink manuscript – Collection Care blog
When paper is badly degraded, and especially when there has been mould damage as with the document below, it often needs to be washed. Washing paper helps to remove acidic degradation products and reforms the hydrogen bonds in the paper structure, making it stronger.
Iron gall ink
Iron gall ink was the primary ink used in Europe from the middle-ages right into the 19th and even 20th centuries. It was often homemade and there is a huge variation in recipe, but its principal ingredients are tannins (usually extracted from oak galls), iron sulphate (also known as vitriol), and water. The different recipes result in inks with different levels of chemical stability, but in most cases there will be an excess of sulphuric acid and free iron (II) ions present, which result in a degradation phenomenon known as ink corrosion. Documents written using iron gall ink are very vulnerable to moisture, which can accelerate the degradation process.