Die corrosion on a proof die?

[Roller]

I'm assuming this is die corrosion but am open to other opinions. If it is, how could this pass undetected on a proof die? (That's a rhetorical question.)

[Petespockets55]

It doesn't really look like most pitting I'm use to seeing.

I'm wondering if it could be debris that has damaged the die around the letters and numbers.
The anomaly on the 6 looks incuse so maybe that is greasy metal dust that has filled that part of the 6 on the die and kept metal from flowing into it?

[mustbebob]

I was gonna say basically the same thing. Are we sure this isn't a struck through of some sort? I couldn't see a proof die pitting like that. The flow marks indicate an MDS coin too.

[Roller]

I was gonna say basically the same thing. Are we sure this isn't a struck through of some sort? I couldn't see a proof die pitting like that. The flow marks indicate an MDS coin too.

I'm open to the struck through idea but I can't conceive through what. Also note the anom. at LIB which does not affect the letters as the date is affected.
Also need to mention that the anomaly outside the devices is raised whereas the anomaly inside the 6 is incuse.

[Petespockets55]

I'm open to the struck through idea but I can't conceive through what. Also note the anom. at LIB which does not affect the letters as the date is affected.
Also need to mention that the anomaly outside the devices is raised whereas the anomaly inside the 6 is incuse.

That's why I was thinking die damage on the raised spots (in the fields) and gritty grease on the 6 keeping the metal from filling that part of the 6. I wouldn't be surprised if it was debris laden grease left over from polishing the die and the worker not cleaning the die face before putting it back into service.

[mustbebob]

I agree. The grease is bad enough, but when little bits and pieces of dirt, grime, metal and other things get mixed in with it, some of the resulting struck throughs are amazing. Die damage is possible as well. It is just so hard to figure some of this stuff out unless you have been there and saw the process.

[Roller]

Do not all struck throughs produce an incuse result? (Unless the foreign material is still attached).

[Petespockets55]

Do not all struck throughs produce an incuse result? (Unless the foreign material is still attached).

I believe that answer is yes, which is basically what we see on the 6. The raised parts on the fields next to the devices are what I'm perceiving as die damage.

As the die struck more coins and the grease inside the 6 dissipated, the incuse part on the 6 would go away but the raised bumps (from die damage) around the devices would have remained.

[willbrooks]

How do you know that this came from a proof die?

[Roller]

How do you know that this came from a proof die?

It appears to be a proof coin. Wide squared rims; some frosting on devices; and mirrored finish in field. That's the coin but it may have been struck with a new business die I suppose?
May be one of those rare SMS coins.