What Kind Of Error Is This?

[Marchas45]

I just bought this coin on e bay, it's a 2007 John Adams proof coin. What's your opinions on it? to me it was a neat buy but then again I've never seen anything like this especially in a proof. Anxiousely waiting your thoughts, would it be a rotated die and filled die? Marchas45

P.S. the third picure has scratches on the coin holder not the coin

[diamond]

At first I thought it was an in-collar double strike with slight rotation between strikes. But if that were the case, the frosted surface of the first-strike design elements would have been largely or completely obliterated. Here the frosting is fully intact. If the frosted design elements are exposed by a stencil of some kind, with the field protected by the same stencil, then you could get this pattern if the stencil shifted. How would you like me to write it up for Coin World's Collector's Clearinghouse column? If you're interested, contact me at mdia1@aol.com. -- Mike Diamond

[Marchas45]

At first I thought it was an in-collar double strike with slight rotation between strikes. But if that were the case, the frosted surface of the first-strike design elements would have been largely or completely obliterated. Here the frosting is fully intact. If the frosted design elements are exposed by a stencil of some kind, with the field protected by the same stencil, then you could get this pattern if the stencil shifted. How would you like me to write it up for Coin World's Collector's Clearinghouse column? If you're interested, contact me at mdia1@aol.com. -- Mike Diamond

Sure Mike you can write it up. Reading your reply are you saying it's a fake made with a stencil? or made when the stencil shifted when it was made? LOL I'm lost.

[diamond]

Sorry if I was unclear. This is a genuine die preparation error. The stencil I was talking about would have been used during the final step of die preparation when the frosting was applied to the recesses of the die by the mint technician.

[clairhardesty]

Mike, I don't believe a stencil is used with the modern lazer system. What this most likely is is a misalignment of the die in the lazer system or an offset error of the lazer itself (possibly caused by an image recognition error in locating the die position and rotation). I work in the semiconductor field and we use image recognition for a variety of tasks that are similar to what might be used for laser balsting the frost on modern die. A task that is extremely similar is wire bonding of semiconductor "die" in a package. The wire bonder uses image recognition software to determine the exact location and rotation of the die and the package inside pins and then rapidly stitches the wires from the die pads to the package pads. Occasionally the image recognition sees something that it mistakes for the intended alignment marks and the wires miss their marks. I have included a close up of the lazer pattern on a 2009 proof coin (at about 1 micron per pixel) in which you can see the hemispherical bumps that result from their opposites in the die. Note how the spot size is varied along with using a psuedo random location scheme to simulate real sand balsting.

[diamond]

A misalignment of the laser is certainly possible. I need to do some research to see when laser frosting was introduced to Presidential dollar dies.

[clairhardesty]

I just looked over my Presidential proof sets and 2007 is definetely a lazer frost. Interestingly, it only appears to have been in use on the Presidential dollars and the quarters at first. It looks like the lazer only came into use for the other coins (cent, nickel, dime, half, and NA dollar) in 2010. There is a very distinctively different look to the finish under magnification. The lazer not only has a large spot size (which as I said seems to be getting larger recemtly) but also tends to show some patterning on large areas of frost. This can be an artifact of using a pseudo random pattern over a large area because a pseudo random pattern really does repeat. This artifacting worsens as the spot size increases and the complexity of the randomization algorithm decreases (two things that are used to reduce time spent on the frosting machine).

[diamond]

Thanks so much for this additional information.