Variation of Densities and Refractive Indices in Tempered Glass

A knowledge of density distributions in tempered glass is helpful in better understanding the tempering process. Since the densities and refractive indices of a glass are uniquely related, density distributions were determined by a schlieren technique which gives a direct measure of index gradients. The advantages of this nondestructive approach are that it yields the location of each density fraction within the glass and that it is equally applicable to fragments and whole pieces of tempered glass. Thus, it also allows observation of changes in local densities which accompany fracture and the release of internal stresses.