» Effloresce redirects here, for the album by Oceansize, see Effloresce (album). Efflorescence, in chemistry,'s the loss of water (or a solvent) of crystallization from a hydrated or solvated salt to the atmosphere on exposure to air. Examples A 5 micrometre aqueous droplet of NaCl will spontaneously crystallize at 45% relative humidity (298 K) to form a NaCl cube by the mechanism of homogeneous nucleation. The original water's released to the gas phase. Gypsum (CaSO4.2H2O)'s a hydrate solid… (More on Efflorescent)