One can also add 1 cm3 of formaline or phenol . Insofar as concerns the uses of gums arabic in preparing the lithographic surface, in metallography, and in preparing the light sensitive surface in photography, turn to the articles on lithography and on photographic processes . The coagulated sap of various tropical trees. It can be dissolved in heavy benzine to obtain a thick plate which is then thinned with cristallizing benzine. This type of resin is produced by tropical trees which are mostly found in Madagascar.
Real copal is hard.
Copal is used in graining in aquatint , in various galvanic processes , and, in particular, in making hard grade lithographic crayons. Colophony is made by distilling pine tree resin. It is a by-product of turpentine oil. The latter being more fluid flows downward leaving behing the resin. However, it is not advisable to use it on aquatint plates.