New materials used for paper conservation should not be used unless the user has a full knowledge of its defects. The purpose of this paper is to show how many of the defects of a material can be detected with simple apparatus so that the user can more easily reject the not obviously bad. The major vices of a material intended for use in the conservation of library material are: 1) incorrect acidity; 2) liability to discoloration or fading; 3) liability to cross-linkage and insolubility; and 4) tendency to strain on drying.