Once it was practiced by many fine lithographic print houses in Europe and America. Until recent years it was the most delicate process and the only process of producing high quality photo-realistic prints on regular paper. Today just few professionals know of its existence. Try searching for collotype on the Internet. The basics of collotype.
All dichromates are poisonous.
When working with them in liquid form use rubber gloves and glasses. In handling dry crystals use gauze mask. 10-12 mm thick glass plate grinded with sand paper. F. Use the rest of water for making Potassium Alum solution. Then add it to the gelatin stirring well.