Collotype, known as 'phototype' in France and 'lichtdruck' in Germany, came into use in the 1870s. It has the advantage of being able to render continuous gradations of tone without the intervention of a screen, but its disadvantage is that the plate can only yield about 2000 impressions. For these reasons collotype is usually only used for work where the accuracy of the tone is of special importance, as in the reproductions of works of art.

Collotype is a photomechanical process in which a film of gelatine provides the printing surface. The technique depends on the fact that light-sensitised gelatine hardens in proportion to the amount of light to which it is exposed.

A solution of light-sensitised gelatine is poured over a sheet of plate glass. When it is dry the plate is placed in contact with the negative and exposed to light. The dark parts in the original image (light in the negative) cause the gelatine to harden and become impervious to moisture, while the light parts in the original (dark in the negative) remain soft and absorbent. When the printing ink is applied to the gelatine it is accepted in inverse proportion to the amount of moisture the surface retains, the driest areas accepting most and therefore printing the darkest. The printing surface is formed of a massing of tiny irregular crinkles created as the gelatine dries in the initial plate-making process. To print a collotype in colour, a separate plate is required for each shade. Collotypes are often also coloured by stencil.