Testing for Iron-Gall Inks
A simple and efficient method for the analysis and comparison of inks is thin layer chromatography (TLC).

In order to separate the various carboxylic and phenolic compounds that may be contained in iron gall ink, the mobile phase should be a polar solvent (e.g. ethyl acetate) or solvent mixture and made acidic (e.g. by adding formic acid).

The coloured spots can be compared under normal lighting; other spots may be detected under UV light. The phenolic compounds may be made visible by spraying with $\ce{FeCl3}$ solution.