It is not always possible for the conservator to identify the type of ink used purely by sight, especially as ink recipes varied enormously. Iron gall can often be mistaken for bistre ink as the tone can appear very similar. A UV light can be used for further scientific non-destructive analysis. For example, strokes of iron gall ink are more opaque than bistre ink and will not generally fluoresce, but appear darker.
Iron gall ink is very acidic in nature. It can fracture the paper causing minor losses, fade, and it can bleed from the one side of the paper to the other. The area where the ink has retained a dark, rich colour is the area of the paper most likely to be fragile.
The conservation of iron gall ink poses a challenge to the conservator as it is made complicated by the differing ratios of the inks primary ingredients: water, galls, gum tannin and iron or copper sulphate.
Take a look at case study of XVII/4, Palazzo Valmarana and see how the iron gall ink has damaged the paper. Find out about the conservation treatments which are able to reduce this.