Show zinc causes paint to show color variation A mans puzzlement over a fence post which he bad painted black but which turned white every night wag the starting point of a program of research which has culminated in the discovery of a number of chemicals having this remarkable chameleon like property termed information regarding these chemicals has now been made public by the american chemical society the famous fence post waa painted with a pigment having a zinc basis it would turn black soon after each morning only to turn white again when darkness came tinny explanations have been given for th phenomenon but cleatus clea tUu are not yet agreed as to the cause of it they have however found sev eril other substances besides the zinc sulfide which ans tn the paint on the post that will also change color with the light most of the known phototropic liquids are solutions of color less derivatives of certain dyes the solutions are practically colorless in the carh bat turn the color of the parent dye when exposed to light |