A study was conducted using atomic absorption spectrophotometry to evaluate the extent of removal of silver, copper, mercury and gold from daguerreotype plates during solution cleaning. The first part of the work compared the two main types of daguerreotype cleaning solutions referred to in the photographic and conservation literature: acidified thiosulphate (nh4) 2s2o3) and acidified thiourea (cs (nh2) 2). Thiourea solutions were shown to be preferable because of their relative selectivity in removing ag2s tarnish with minimal damage to the base plate. A second part of the study considered the effect of varying the strength and acidity of thiourea solutions on the removal of mercury and gold. Preliminary recommendations can be made toward the optimization of thiourea / acid concentration in the cleaning solutions.