kept in portfolios made of heavy wrapping paper (chosen for its pliability and resistance to wear as well as tested for its purity), and tied up with dark tape. These portfolios are very useful and cheap, and serve to protect the prints in some measure from dust. They should never be used on open shelves, however, but only in dust-proof cabinets. The larger size prints, for convenience in classification, need to be held together in some fashion, and may be simply laid between folds of large wrapping paper. These large prints are conveniently kept on trays which should not be too deep; 1½ inches in the clear is a good height. Cases with trays should be built so that the trays can be pulled out when the doors are open at an angle of 90°. This is important, as it is very often desirable to open two neighboring cases at the same time, and if the case is built so that the doors must be open at an angle of 180, this is impossible. The same method of fitting the doors to keep out dust which was described above (see p. 149) may be used in these cases. All paper is subject to attack by insects, and the curator of prints may at any time find that he has overlooked a diseased print which is spreading trouble among the others in his collection. For this reason one of the finest collections in the United States has gone to the expense of having its cases lined
