Tapering/thinning of peripheral devices explained

[willbrooks]

A couple of folks asked me about this study, and so I will post an abridged version of it here for the community. We had a question on the forum here from someone asking about some thin/tapered letters on 1996D cents that he was finding in mint sets. He was convinced the difference in the letters was a new design variety. Despite assuring him that I had seen this on several different dates and on various areas of the periphery, and was therefore either due to an incomplete hubbing, or else over-polishing of the die, he was not convinced and was still insistent that it must be a design variety. So, I got the coins from him and studied them, and then sent them to Ray Parkhurst for him to photograph in 3-D rendering. The results were quite conclusive that, in fact, this effect was indeed caused by over-polishing of the field in that area. 1st and 2nd pics are of the "thinned" coin vs a normal coin of the same date.





Now, in this last image, Ray did an inversion of the image so we are actually seeing what the dies would look like, rather than the coins. Here we have our “smoking gun” as Ray put it. With this incredible technique, we can see that the die near the rim on the coin with the thinned devices is clearly compromised compared to the “normal” die.




I was able to find and photograph a couple of others from different dates with the same effect going on. Here is a 1989 with the same thing.



And here is a 1986 with thinning on ONE.




And here is an example from the coppercoins listings.
http://coppercoins.com/lincoln/diest...&die_state=mds

If you search a lot, you will find these, as well as thinned out FGs, etc.

I am glad this came up as this is a nice precursor to the other study we have just completed, and on which I am still awaiting word.

[Petespockets55]

Thanks so much Will. The progressive "animation" on those images make it easy to see the changes to the die face and how those changes show up on the coin surface from polishing to "clean up" the dies to make them last longer.

[jfines69]

Thanks Will and Ray... I like those... On the first 2 images you can not tell there is a ridge ring developing on the over polished die... In the inverse 3D image you can clearly see the ridge ring running thru the thinned portions of the letters top ends!!!

[willbrooks]

Thanks Will and Ray... I like those... On the first 2 images you can not tell there is a ridge ring developing on the over polished die... In the inverse 3D image you can clearly see the ridge ring running thru the thinned portions of the letters top ends!!!

Jim,
A ridge ring is a form of die deterioration caused by the cold flow of metal toward the rim during the striking process. That is not what is happening here. This effect is the result of overpolishing of the die when it was made, before it ever even went into service. What you are seeing here is the lowered level of the field as a result of this polishing.

[jfines69]

Jim,
A ridge ring is a form of die deterioration caused by the cold flow of metal toward the rim during the striking process. That is not what is happening here. This effect is the result of overpolishing of the die when it was made, before it ever even went into service. What you are seeing here is the lowered level of the field as a result of this polishing.

Thanks Will... Looks like a ridge ring was forming and then got caught up in the polishing... Always learn something new every day!!!

[willbrooks]

I just found another example, again on a 1986 reverse on ONE, but not quite as extreme as the one pictured above.

[willbrooks]

Thanks for the timely bump, Ed. This will actually be an article in the upcoming July 2020 Errorscope.