A history of the deterioration of the earliest known daguerreotype portrait, of Dorothy Catherine Draper, 1840, left in the Hands of Dr. Robert Taft, Associate Professor of Chemistry, University of Kansas. The heavily oxidised plate was restored to 50 percent of its original blackness by immersion in acid thiourea until no further change was visible, twelve minutes, then rinsed in distilled water, dried in methanol and in a current of air. The thiourea solution contained 70 g thiourea in 250 cc distilled water, 0.8 cc phosphoric acid, 0.2 cc non-ionic wetting agent, additional distilled water to 500 cc. The used solution, analysed by atomic absorption spectroscopy, contained no silver, no mercury, lots of copper.