Knives, forks, and spoons made from a biodegradable starch-polyester material. The photo has been realized using the photoelasticity method, an experimental method which gets a fairly accurate picture of stress distribution even around abrupt discontinuities in a material.When a ray of plane polarised light is passed through a photoelastic material, it gets resolved along the two principal stress directions and each of these components experiences different refractive indices. The difference in the refractive indices leads to a relative phase retardation between the two component waves.The setup used to photograph this photo was probably composed of:A regular light source, with a quarter-wave plate installed to polarize the emerging lightA regular photo camera, with a quarter-wave plate installed in front of the lensLight and camera being installed and oriented in the same direction, the twoquarter-wave plates were turned with the polarizing axis in the same direction.