The effect of tin on some physical properties of the bottom surface of float glass and the origin of bloom

The surface composition of the tin side of float glass has been investigate d by XPS and found to contain a large quantity of till in the near surface region resulting in an increase in refractive index and viscosity Transmiss ion Mossbauer spectroscopy was used to examine tinted glass and the oxidati on of Sn2+ to Sn4+ was found to take place on heat treatment as in clear gl ass. Conversion electron Mossbauer spectroscopy was applied to both cleat a nd tinted glasses and showed that tinted glass had a greater proportion of Sn4+ and that both clear and tinted glass showed faster conversion of Sn2to Sn4+ in the near surface region on heat treatment. Bloom was only seen o n glasses for which this conversion occurred at a temperature where the sur face viscosity, was sufficiently low for wrinkling to occur: Tinted glasses were found to be less prone to bloom than clear glasses. This was attribut ed to their greater proportion of Sn4+ in the near surface region before he at treatment. This may result in a smaller change in thermal expansion and in a higher viscosity making wrinkling less likely.