"milk Spots" On Aluminum Coins?

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Author	Replies: 5 / Views: 1,093
NumisEd Pillar of the Community United States 5209 Posts	Posted 12/16/2022 09:36 am I've got a couple of aluminum coins from a 1973 Nepalese Mint Set that show white ("milk") spots on each of them. See photo below. I am not sure what these spots are, but I am currently soaking these coins in acetone to see if I can remove these spots. Any other suggestions as to what these spots might be and how to remove them without damaging the coins (if at all possible)? Report this Post to the Staff

John1 Moderator United States 56855 Posts	Posted 12/16/2022 11:19 am If they are "milk spots" they are forever. John1 Report this Post to the Staff
oriole Pillar of the Community Canada 5271 Posts	Posted 12/16/2022 12:21 pm That is corrosion. Aluminum oxide, used as an abrasive, and quite insoluble in anything normal. Report this Post to the Staff
HondoB Bedrock of the Community United States 26111 Posts	Posted 12/16/2022 12:43 pm Would VerdiCare help with this? I have some aluminum tokens with corrosion. VerdiCare may not remove it, but would it slow the spread? Inordinately fascinated by bits of metal with strange markings and figures Report this Post to the Staff
NumisEd Pillar of the Community United States 5209 Posts	Posted 12/16/2022 12:56 pm Quote: That is corrosion. Aluminum oxide, used as an abrasive, and quite insoluble in anything normal. If so, then I have to be a bit more careful buying aluminum coins. Report this Post to the Staff
oriole Pillar of the Community Canada 5271 Posts	Posted 12/16/2022 4:50 pm Aluminum is an extremely reactive metal, but under normal circumstances quickly forms a protective layer of transparent aluminum oxide when exposed to air, so aluminum coins (like aluminum foil) normally can stay shiny for a long time. I am not familiar enough with the process to tell you when this protective coating will fail, but mercury will prevent the coating from adhering. I'm sure that Wikipedia has a lot to say. Report this Post to the Staff
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