These glass drops were formed by heating a glass rod with a gas burner. The molten glass then fell into a basin of cold water, subjecting it to intense heat shock. The surface glass solidified more rapidly than the center glass, resulting in surface tension towards the center and significant mechanical stress. These constraints make the glass anisotropic and birefringent. When a ray of light crosses a constrained photoelastic medium, its polarized components encounter different refractive indices, which will produce a relative phase delay of the components, hence the observed colors. Linear polarized light entering the tears will be transmitted with an elliptical polarization at the output. For this photograph, the assembly consisted, in order, of a white light source, a linear polarizer filter, glass tears and a polarizing filter perpendicular to the first. The dark background is caused by crossing the filters.