When certain stressed crystalline subjects are placed between crossed polarizers the stresses change the polarization quality of a light beam transmitted by first polarizer. This is change is related to the degree of stress in specific locations. Some colors align with the second polarizer while others are blocked and thus eliminated from the original light and these areas become colored and indicate the presence of embedded stresses in the sample. In these photographs a glass disk is subjected to increasing degrees of compression by the C-lamp.