Not sure what caused this on a proof

[Luvncoins]

Please take a look at the top of the wheat on the left side of the coin. Found this while looking at my proof sets, didn't think it could be from grease because it is a proof set. Is it possible that it is from grease if not, then what could have done it? And it is worth breaking up the set? Thanks for your help.

[jcuve]

I believe you're talking about the small loss of detail in the upper left wheat stalk. A struck through filled die seems the most likely explanation. It could be grease or some other kind of gunk that got into a small part of the die face. Not really common on proofs, but I am not sure the area effected is big enough to break up the set for the error. Nice find and thanks for posting!

[mustbebob]

I agree with Jason. I would also add that a grease struck through is possible whether the coin is a proof or not. The same machinery still strikes them.

[Luvncoins]

First of all I want to thank you both, wish I had the option of marking both as the best answer. For some reason I had mistakenly thought that proofs were struck on different machines than normal coins, nice to learn something everyday! I will be so glad when I am able to look at a coin and know instantly when and what exactly is wrong...maybe after a million?? LOL, thanks again.
Laurie