1) Opal 
• (n.) A semitranslucent variety of opal that becomes translucent or transparent on immersion in water.
(from the article `opal`) ...may crack or lose its colour if it dries, many finished stones are protected by water or films of oil until they are sold. Opals absorb liquids ...
Hy'dro·phane noun [ Hydro- , 1 + Greek ... to show, appear: confer French hydrophane .] (Min.) A semitranslucent variety of opal that becomes translucent or transparent on immersion in water. 
Hydrophane is a porous, translucent opal, which on being placed in water becomes nearly transparent as the water is absorbed into the pores.
hydrophane 1. A semitranslucent variety of opal that becomes translucent or transparent when immersed in water. 1. An opal that is almost opaque when dry but transparent when wet.
a partly translucent variety of opal, which becomes more translucent or transparent when immersed in water.