Cobalt chloride test paper turns pink when it is exposed to water or moisture. The blue form is cobaltous chloride dihydrate. The pink form is cobaltous chloride hexahydrate. read more
Cobalt chloride paper can be purchased in premade sheets, but it can also be made by dipping paper into a cobalt chloride solution and letting it dry. As humidity increases, cobalt chloride will shift from blue to pink, with a purplish color serving as the mid-phase hue between these two colors. read more