Photographers' Formulary Gum Arabic (Liquid) is used in Bichromate printing.
Note:
Gum Arabic is used to slow down the absorption of the ink into the paper, so that the ink dries more on the surface, giving a more intense color. It also imparts a glossiness to the dried ink. Gum Arabic was used for a similar purpose in some photographic formulae and was also the basis of the gum bichromate process popular among pictorialist photographers around 1900. It is also enjoying a revival in recent years among those interested in handmade photographic papers.