Carbon spot

So I acquired a Silver Eagle with a carbon spot. The name is because it’s black, but the blemish is sulphur dioxide. After consulting Google, I tried the baking soda and tin foil trick. I’m impressed. Black spot gone, although a pale corrosion blemish remains. It could be polished out, but I think I’ll leave it as is. Thoughts welcome.

Oh WOW! you did a great job of that. Dang really impressed

I've never heard of carbon spots on silver coins before :O

@AceBullion or anyone, any idea why this occurs?

Not sure how they appear on coins @kimchi , but they (or something that looks very similar), can appear on flatware and holloware ( cutlery, plates, bowls etc.) and the usual cause is salt or some slightly corrosive sauce not being washed off quickly enough. They are virtually impossible to remove.

kimchi wrote:I've never heard of carbon spots on silver coins before :O

@AceBullion or anyone, any idea why this occurs?

@kimchi I am speculating here, but the tarnish spot seems to be sulphur dioxide. Hence why it cleaned up so well with baking soda. But sulphur dioxide usually manifests as toning, not a dark spot. My theory is that it’s due to how the coin was stored. Humidity, paper, wood etc with sulphur (from the atmosphere or paper) that has oxidised. The speckling around the spot looks like something may have splashed on the coin and the corrosion followed the splash pattern.

ArcaneCollector wrote:

kimchi wrote:I've never heard of carbon spots on silver coins before :O

@AceBullion or anyone, any idea why this occurs?

@kimchi I am speculating here, but the tarnish spot seems to be sulphur dioxide. Hence why it cleaned up so well with baking soda. But sulphur dioxide usually manifests as toning, not a dark spot. My theory is that it’s due to how the coin was stored. Humidity, paper, wood etc with sulphur (from the atmosphere or paper) that has oxidised. The speckling around the spot looks like something may have splashed on the coin and the corrosion followed the splash pattern.

none of my other coins have this, And storage is always controlled with temp etc. I might have got that coin from someone at some point but have no idea why that one had that spot. 

I have boxes of weird and wonderful things that I have bought from people ... even graded coins that developed marks after being slabbed. Usually it is Milking that graded coins suffer from... But yeah.. a odd one.