That's a stain. The last possible RPM was in 1989. It was then that hand punching the MM was ended and therefore it is impossible to have a RPM on anything dated 1990 and newer. Value 1 cent.
1 Cent . I was gonna say Flat field doubling at best , but yes it does look like a stain in the shape of a D .
The mark below the mm is probably a small plating blister if it’s raised. While it vaguely resembles a D, it’s not the same size or shape as the mm. That’s the obvious giveaway that it can’t be a RPM (besides the fact that mintmarks weren’t added by hand in 2017) If you’re referring to area to the right of the mm. it looks like some very minor die deterioration doubling and is very common on copper plated zinc cents.
Definitely a Stain plus plating blisters. Just in case you didn't recognize all the other plating blisters I circled them in yellow. If you didn't notice the stain went up and on the lower part of the D too shown in Blue. And the D has split plating / die deterioration issue in Green, you can see the metal stretching on it's right and lower right, and the inside of the D. The cent has lots of problems.
Can you educate me. How do these blisters occur . Is it in the making of the planchets ? Are these rolled out today or do they receive the Blanks already cut ?
planchets are bought from an external supplier they are very thin copper, I think 7 micron thin, copper plated zinc cores. Zinc reacts when plated with copper to such things as .. ooh steam (like if it goes through the laundry); left on the ground .. you know... standard use stuff. The coins are designed to be easily and low cost manufacturer, period for visual identification as one cent by cashiers, et all. They are not designed for "collectors" especially the ones designed and manufactured for circulation. Any time there is a breach in the copper surface you will start getting corrosion. minor PMD can cause a breach. Split plating from die deterioration can cause a breach. scratches or other surface damage can cause a breach. This corrosion can spread internally and start bubbling, linear plating blisters and a whole bunch of issues. Just know that a copper plate zinc planchet has corrosion domes, plating blisters (which include long linear ones). So many problems .... I was going to PM you something but your PM is turned off.
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Is this right? Seems pretty thin to me. 7 microns is about 28 ten thousandths of a inch. You would need 218 of those 7 micron thick planchets to stack up to the thickness of a U.S. penny.
I've read 7 and 8 micron thin copper plating; plating which is over a zinc slug which is our current Cent mid 1982 to current. ie, you start out with a zinc slug. Then you copper plate it with 8 microns of copper plating. There is no layering. With mid 1982 and earlier it was a copper planchet. I've also read stuff about 20 to 25 micron but I think those are related to strictly the Royal Canadian Mint's version of the modern cent. https://www.governmentattic.org/31docs/MintCoinageAltMetalsStdy_2012.pdf
