After having been kept in the dark at relative humidities of 75, 55 and33% respectively, for one and a half years, azurite and malachite mixed with glue discolored, and the higher the humidity, the darker they became. When they were exposed to ultraviolet light the discoloration increased. When irradiated with ultraviolet ray, the glue film lost some of its moisture content, and sometimes its molecular structure was destroyed. Relative humidities ranging from 60-70% were found to be optimum for glue. For pigment layers containing glue, deterioration of the pigments decreased when relative humidities were below 55%. Japanese papers were markedly strengthened when coated with glue. -- AATA