B. Definitely B. When I see the gear cogs I stop listening and mentally turn each gear in my head. If the gears don’t turn properly, I imagine various gear reconfigurations until they work effectively. I can’t not do this!

Thanks Mike!

That’s what I think. It has to do with the depth of the oxide within the copper, which is controlled by the amount of heat. Wavelengths of light reflect off different oxide layers and can interfere with each other, resulting in subtraction of some wavelengths/colors.

got some answers. 1. metalworking shop; 2. I braze/weld copper for some sculptures. Sometimes the copper gets so hot a molten drop falls and goes splat on the floor; 3. The different oxidation states might be from how quickly they cool eg. if they land on the metal welding table vs the floor.