- The wet gelatin is a compound very sensitive to the temperature. It liquefies in 86 ° F approximately, where from the difficulties maintaining a resistant, not sticky coat, and wet remainder by the strong hot season. For the preparation of the mixture, the gelatin can be put in the water-bath to 160 ° F directly without preliminary putting to be dipped into the water, and to be so dissolved at the end of a few minutes (shake during all the duration of the preparation, but it is frequent to luter against lumps). The ideal remainder however the swelling of gelatins during 3 hours at least in cold water, before it put in the water-bath, because the experience shows that you should not too much heating gelatins (their behavior is modified when there was too important rise of the temperature during the preparatory operations – the ideal seems to exceed never 130 ° F in each of the phases of the preparation and the drying). With or without preliminary swelling, to continue the operations by putting the mixture water / gelatins in a bowl, in the water-bath, and to go(take) up in temperature until approximately 120 ° F.
Once well dissolved gelatin, to add the quantity of dichromate, to mix with a glass agitator, then to put leaking out through a filter of paper (filter placed in a funnel) in the drying chamber preferably so that the mixture stabilizes in the exact temperature of the steam room (105 ° F), and patches on which it is going to be poured. This uniformity of the temperature is one of essential conditions of the success of collotype.- Filtered solution, which has to no contain air bubble, can be immediately poured on plates.