Laser characterization and cleaning of 19th century daguerreotypes II

Abstract Recently, we have made tremendous progress in the spectroscopic analysis and laser restoration of tarnished daguerreotypes. L aser i nduced b reakdown s pectroscopy (LIBS) has been applied for the first time to both modern and 150-year-old daguerreotypes. In addition to surface and depth profiling, the analysis of colors on “tinted” samples allowed identification of the pigment. These results complement the previous analysis by laser ionization mass spectrometry of the surface composition of clean and tarnished examples of the old photographs. Laser ablation cleaning of the submicrometer tarnish layers has now been clearly demonstrated on numerous daguerreotypes with various extents and types of tarnish. The use of computer controlled XY translation and stable laser beam quality have allowed decisive proof-of-principle examples of laser restoration. The best parameters of laser wavelength, power and pulse duration have been determined. Using digital files of daguerreotype images, straightforward models have been developed that allow for the digital mapping of the surface tarnish. In principle, such maps could guide the computer control of the laser cleaning process.