Submit your questions for Ben in the comments section for a Q and A session next week. Heating zinc oxide with a blow torch causes it to turn from a white powder into a golden yellow. The process reverses when the substance cools back down to room temperature. The heat drives out some oxygen from the ZnO lattice, cause some locations to have a Zinc metal ion. This disruption in the lattice is able to absorb more blue and violet light, causing the overall substance to look yellow.