AbstractA number of cellulose nitrate‐base cinematograph films have been examined, many of which are twenty or thirty years old. Reactions between decomposition products of the base and gelatin had in some cases caused the emulsion layer to become sticky with loss of the contained silver image. Since films in this condition cannot be duplicated, it represents a total loss of record. This can now be avoided by subjecting the film to certain tests, the results of which give adequate warning of the onset of the critical stage, thereby enabling the film to be duplicated while still in good physical and optical condition. The application of these tests has been incorporated in a scheme of surveillance devised for use with stored fil