Jeff,

I think we talked about this already last time that the one at Bonhams was sold.

It has nothing to do with heat, like Nathan suggested. But it's a good guess when you actually look at the "damage".

18kt gold consist of 750 parts pure gold (24kt), and then 250 parts are added, mainly copper and silver to obtain the yellow gold color. (18kt white gold has thesame 750 parts of pure gold, but then instead of copper and silver...you have to add palladium). Ofcourse there are a lot of different gold mixings and colors. Most common we know are yellow, white and red/rose gold.

Pure gold has very high resistance to oxidization. Silver and copper do not.

Now, the effect we see on the surface is no actual damage, it's just some "oxidation". The copper and silver parts in the mixture are quite prone to oxidate when in contact with air. So, that's it. We often see this with gold watches and especially in the areas which we can see but where no friction/wear takes place, so the gold has "time" to oxidate (around the pushers, between the lugs,...). 18kt gold oxidates very slow and only very little, so this would suggest that this watch was not worn in the recent decade or so (or only very very little), otherwise we would see no oxidation at those places (on top of the case which is very submissive to friction and contact with clothing).

This effect can be perfectly "cleaned" either by a special cleaning cloth (like we know for cleaning silverware, there also exists thesame for gold) or a very very light polish.

Hope this helps a bit,
All the best,
abel.