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Message:: [QUOTE="desertgem, post: 762324, member: 15199"]Doug, I did not deny that there could be a color difference/change in gold, just that it is a change that is not due to a "chemical reaction" of gold with something like a sulfur or oxygen component, that is unlikely to reverse itself spontaneously.  Gold doesn't combine with surrounding non-gold atoms under earth surface conditions, but it can be "affected" by surrounding molecules to change it's color as long as those surrounding molecules are there in that state. It is similar to Alexandrite, a gemstone that is naturally green in high energy daylight and red in low energy artificial light. The color depends on the photons energy ( color) re emitted as electrons change positions within atoms of the crystal. The crystal change wouldn't be described as toning. Theoretically, gold is only that yellow color on the surface where light can reach. Underneath it would have no color, as photons could not be reacted. We don't care since we can only see the surface. I don't know what word might be used instead of "toning" for gold. That is why I wrote the sentence, not to be a smart***. Maybe "toning" is a good enough word. I just wanted to say that the color change that can occur with gold is not the same as the color change that occurs with chemical reactions such as sulfur, or oxygen, where bonds are made ( such as with copper or silver, etc.). Jim[/QUOTE]