REDUCTION OF COPPER IN SODA LIME SILICATE GLASS BY HYDROGEN

The reduction of copper in soda-lime-silicate glasses by hydrogen was measured as a function of time and copper content within the temperature range 440 to 650-degrees-C. Copper is reduced to the metallic state in a surface layer whose thickness increases with time and temperature and decreases with copper content. A well developed periodical precipitation of copper particles is observed in the reduced layer. The reduction is accompanied by an alteration of the glass composition in which there is an increase of the copper content and a reduction of the calcium content. The growth kinetic of the reduced layer, followed by optical spectroscopy and measurement of the layer thickness, is analyzed with regard to the tarnishing model.