Most Daguerreotype images show violet discoloration in their shadow areas, which is known to be caused by hydrogen sulfide. The author tried to remove the discoloration using cyanide baths, thiourea-phosphoric acid baths and thiourea-citric acid baths. The cyanide bath removed the photo image as well as the discoloration, whereas the thiourea-phosphoric acid bath and the thiourea-citric acid bath removed the discoloration only to leave the test piece very clean. -- AATA