Patent ID: 8137744

Claim:
A method of manufacturing a label that changes color when put into contact with water, comprising steps of: (a) providing a substrate which is made of a water absorbing substance, said substrate comprising a piece of paper selected from a group consisting of at least simile paper and enamel paper; (b) forming an ink zone on a first surface of said substrate, said ink zone having a color that is identical to color of said substrate and made of a hydrophobic substance, said ink zone being smaller than said substrate in size and shaped into desired words or patterns; and (c) forming a coating layer on an opposite surface of said substrate, said coating layer being comprised of a water-soluble material that is different from said ink zone in color; wherein when said label is in contact with water, said water-soluble material of said coating layer is dissolved in said water and then absorbed by and retained in said substrate thereby making said ink zone visually identifiable over said substrate.