Considers various reasons for duplicating negatives, particularly the behavior of collodion and gelatine emulsions used in early processes. A number of factors determine the best method of making a copy negative, especially with respect to shadow and highlight densities. Text and graphs illustrate what happens to original densities as they are reproduced through various processes using Kodak film. The duplicating method used at the Chicago Albumen Works, of which the author is co-founder, is described.