1988 LMC- what caused this?

[chuckster 125]

Is this some kind of US Mint error, or is this post mint damage?

Thanks.

[diamond]

It's a mint error. The obverse face was struck through a thin layer of obstructing matter. I'm not entirely sure what the substance consisted of. The sharply defined borders are not typical of "grease strikes". But the texture within those borders is not like a deteriorated die cap.

A lot of strike-thrus are not identifiable as to the substance that caused them. The list of known substances is pretty extensive.

[chuckster 125]

It's a mint error. The obverse face was struck through a thin layer of obstructing matter. I'm not entirely sure what the substance consisted of. The sharply defined borders are not typical of "grease strikes". But the texture within those borders is not like a deteriorated die cap.

A lot of strike-thrus are not identifiable as to the substance that caused them. The list of known substances is pretty extensive.

Thanks again!!!

[billscoins]

This might me a piece of used wet & dry sand paper about 240 gritt? I've seen a simialar look on soft metal when a part is helt in a vise with it during machining.
Bill

[chuckster 125]

This might me a piece of used wet & dry sand paper about 240 gritt? I've seen a simialar look on soft metal when a part is helt in a vise with it during machining.
Bill

Hi Bill:

Do you mean that somehow a piece of sandpaper got stuck on the die at the mint, or that someone sandpapered this coin post mint?

[billscoins]

Hi, Chuck
I think that a piece of sandpaper may have got caught between the plancet and the obverse die during the strike. Someone at the mint may have been cleaning off the buildup of copper (copper is very abrasive and tends to stick to unlubricaned surfaces) on the obverse die and a piece of it may have broke off and got struck thru on the hit.
Bill

[diamond]

There is no reason to suspect sandpaper as there is no evidence of grit impressions. Instead you see fine parallel lines. These are the original lines of the unstruck planchet, which are preserved when a relatively soft material with a smooth texture is interposed between die and coin.

[billscoins]

Mikes, the expert. But I 've never seen strip stock with that looks like it has a surface finish of 250 rms run in a press. The cloth idea sounds good thru I have seen this pattern impressed in metal from used sandpaper.
Bill

[billscoins]

Mike, I was just looking at a group of 1988 cents and I have 3 with the same surface finish. How did this happen? I'm little confused about the process involued??
Bill

[diamond]

If you look at any copper-plated zinc planchet, you'll see fine parallel lines. The same lines exist on the unplated planchet. My guess is that they're lines left by the rollers that roll out the strip or the rotating descaling brushes that clean them. These lines will be preserved in the case of a weak strike or when a coin is struck through a smooth viscous substance like grease or oil.

[billscoins]

Hi Mike,
“If you look at any copper-plated zinc planchet, you'll see fine parallel lines. The same lines exist on the unplated planchet. My guess is that they're lines left by the rollers that roll out the strip or the rotating descaling brushes that clean them. These lines will be preserved in the case of a weak strike or when a coin is struck through a smooth viscous substance like grease or oil.”
Diamond

Now that makes sense. I’ve seen rotary wire brushes used on metal, which have left the same pattern. The zinc could have been brushed before plating and been affected this way. That could produce the consistent pattern.
Thanks, Bill