Do a Google Search " Short-wave UV radiation causes the tin to fluorescence at a frequency that is visible to the human eye. When the lamp is placed on the tin side surface, the tin will fluorescence and produce a milky white image that is visible to the human eye " This site
formatting link
this devicewith no details, but click on links for more infoTS1300TIN SIDE Detection For FLOAT GLASS During the production of float glass, one side of the molten glass comes into contact with a bath of molten tin. Traces of tin or tin oxide metal are deposited on the surface of glass as it is removed from the molten tin bath. This surface of the glass is identified as the "TIN SIDE" surface of the glass. the opposite side of the glass is denoted as the "AIR SIDE". The presence of the tin is invisible to the human eye. Glass processors find it beneficial to know which surface of the glass is the tin side surface, since the tin side of the glass results in a smoother surface (among other reasons). Useful for the production of laminated glass, coatings, screen printing, mirrors and more.