Multilayer colloid formation in soda lime silica glass

Silver and copper colloids are formed on the tin-rich surface of float glass at elevated temperatures via reaction with the tin present from the float process. Optical absorption measurements of samples initially stained with copper and then subsequently stained with silver indicate that the second treatment with silver eliminates the optical absorption due to the copper colloids formed during the first treatment. If silver is applied before copper, both silver and copper colloid absorption bands increase in intensity for initial heat treatments at lower temperatures and shorter times, but no copper colloids are formed if the initial heat treatment produces a very large amount of silver colloids. It is proposed that copper colloids formed during the initial heat treatment serve as nuclei for the subsequent growth of a layer of silver, eventually covering the nuclei of copper with a layer of silver which is thick enough to mask the optical absorption of the original colloids. The reverse does not occur if silver colloids are formed before copper colloids.