[Captain Rhino]

Slow release of gases entrained during the original casting process?

[Recovering_Democrat]

Slow release of gases entrained during the original casting process?

Ah, another plausible idea. Good, Rhino. (Why did you ever choose THAT name?) :)

[Attention Surplus Disorder]

“Slow release of gases entrained during the original casting process?”

Best explanation yet, IMO. Some of the noble metals can absorb or dissolve astounding amount of hydrogen. Palladium, IIRC, can dissolve 500 times its volume of hydrogen. Platinum, similar. Where would the H come from in a crude furnace of over 110 years ago? Reducing atmosphere in the furnace..?