Gelatin is a peptizing polymer.Originally Posted by htmlguru4242
When silver halide is precipitated in its presence, the silver halide crystals are 'peptized' by the gelatin polymer by being surrounded and suspended by the gelatin. If this were not so, the crystals would settle to the bottom of the container. The gelatin suspends the crystals evenly within the solution.
Gelatin cannot be used with cuprous oxide as it is dissolved in strong acid then precipitated in strong base and this pH cycle destroys the gelatin.