Laser ablation mass spectroscopy of nineteenth century daguerreotypes

Laser desorption mass spectroscopy has been used to characterize both moder n and similar to 150-year-old daguerreotypes, Such investigations are a nec essary prelude to attempts to clean them of tarnish and other contaminants by laser ablation of the surface layers, Both positive- and negative-ion ti me-of-flight spectra were obtained following YAG laser ablation/desorption at 1064, 532, and 355 mn, Major peaks obtained from several daguerreotypes reveal expected elements from the substrate (Ag, Cu) as well as the develop ing (Hg) and gilding (Au) processes. Silver clusters (Ag,) may reflect surf ace desorption of molecules or, alternatively, aggregates formed in the eje ction process. Silver sulfide molecules observed from old daguerreotypes ar e the signature of the tarnishing process.