Birefringence
Stresses and stretching imprinted in the manufacture of plastic cutlery, as revealed by variations in birefringence. Defined as a material’s ability to change the polarization of light, birefringence depends on the local stresses in the material and the wavelength of light. By laying the cutlery on a computer screen and imaging through a linear polariser, these stresses thus can be seen. (Picture taken during an outreach event at the University of St. Andrews, U.K.)
—Morgan Facchin, University of St. Andrews