Thinness or want of density in a negative may lie accounted for in two ways - by weak development owing to insufficient proportion of the actual image maker, pyro and metol, and by too early removal from the bath. Thinness is also caused indirectly by over-exposure and by insufficient potassium bromide. With a pyro-metol developer, some time must elapse after the details appear in order to obtain density, even though the picture seems to be veiling over.