It has the advantage that it can render continuous graduations of tone without the intervention of a screen. But the making and printing of collotype plates is skilled and expensive work and can easily go wrong. Variations in humidity are likely to upset the balance of moisture in the gelatin causing it to swell or shrink. The surface is too delicate to produce more than two thousand impressions. For these reasons, collotype has been used for luxury publications and, since World War II, has been largely abandoned for other commercial purposes.
Collotype is a photographic process in which a film of gelatin provides the printing surface.
The technique is dependent on the fact that light sensitized gelatin hardens in proportion to the amount of light to which it is exposed. A solution of gelatin is poured over a sheet of plate glass. When dry the plate is placed in contact with a reverse negative and exposed to light. In proportion to the strength of the transmitted light the gelatin dries and hardens, while the unexposed areas remain capable of absorbing moisture. The surface can then be printed as a lithograph.