Patent ID: 7381506

Claim:
An image forming medium, comprising a substrate; and a mixture comprising a photochromic material and a solvent wherein said mixture is coated on said substrate, and wherein the image forming medium is configured to constrain the mixture in place on the substrate; wherein the photochromic material and the solvent are selected so that: the photochromic material exhibits a reversible homogeneous-heterogeneous transition between a colorless state and a colored state in the solvent; the photochromic material in its colorless state remains dispersed in the solvent, but phase separates from the solvent when the photochromic material is in its colored state; and the photochromic material in its colored state phase separates out of the solvent in the form of opaque, polydisperse crystals; and wherein the image forming medium is configured so that: the image forming medium may undergo image formation and image erasure at least two times; and an image formed on the image forming medium remains stable and visible under indoor ambient conditions for at least two days.