The gum process became popular in the 1890s and gave the photographer a lot of control over how the print looked when finished.
Working methods and formula vary so much that there is no one way to make a gum print, each practitioner finds his or her own way of working. In general a sized water colour paper is coated using a brush with a solution containing gum arabic, a bichromate and pigment (usually water colour). Once dried it is then exposed under a negative to UV light where the gum hardens in proportion to the light reaching it. After exposure, the print is developed by dissolving the still soluble gum in water. Development can be controlled by the use of a water spray, brushes and sponges. Multiple printing is often done to build up density and introduce other colours either from the same or different negatives of the same image. Variations include applying gum onto an already developed platinum or cyanotype print.
…making a gum print can take several weeks and several attempts.