I've noticed this on some of my US and other coins, but this recent acquisition reminded me of this phenomenon. On this 1942-P Mercury dime below, which also happens to be from a rotated die on the reverse, at around the 2-3 o'clock position (above E PLURIBUS UNUM and below AMERICA), there's a separate, small, and circular area with its own cartwheel effect. It appears to be uninterrupted by the larger central cartwheel effect, which in turn seems to be absent in that area. I've also seen multiples of these smaller cartwheel areas on other coins. Is it due to fluctuations in pressure when striking (e.g. due to a rotated die, does the obverse die and the reverse die cause different areas of the planchet to experience elevated pressure levels, enough so that the cartwheel can be found elsewhere from the center?)? Thanks in advance!
A pretty common occurrence on mercury dimes, I believe what you are seeing is the effects of a clashed die.... I think I see other evidence of this in the leaves..... Another possibility, is called ghosting, look this up for a good explanation, I can't give one(it's too far into Miller time) Lincoln Cents sometimes show, an outlier (or ghost) of the obverse devices on the reverse.....which can effect the cartwheel luster
The effect you are describing is called "ghosting". Using that Winged Liberty head dime as an example - During striking, metal is forced into the obverse die which alters the patterns of stress in the metal and the result is that a "halo" of the obverse design is visible on the reverse side (and vice versa).
Yup, ghosting. Some people confuse ghosting for clashing actually. Most often seen on cents and dimes only due to the higher mintage numbers and thickness of the planchets therefore more examples are out there to come across. The kennedy halves are known to be plagued by ghosting as well but it's seen on most series especially those with heavy die use.
Is this more likely to happen with lighter/thinner planchets? Is this typically seen with silver coins or could it be any other type of metal?
^^What he said. And yes, here is a more extreme example of the example above. Had they kept going on that 1982 cent it may have ended up looking something like this:
Yes, it was found in an old box of 1950s and older cents. Other coins within also suffered the machinist's pleasure, but nothing close to the one above.
Back to the reflective luster patches on that Merc dime: I would say that it's a phenomenon akin to chatoyance. Chatoyance is a term from the gemological world rather than numismatics, but it's a similar kind of thing. I suppose it's die polish that causes it on this coin, though maybe ghosting has something to do with the contours of the fields (and therefore the different luster patterns), as @heavycam.monstervam and @dcarr suggested. Ghosting and luster combined could cause that sort of chatoyant look. I guess I just wanted to use the word "chatoyance". It's a cool word. I first learned about it while reading up on fossil shark teeth. Regardless of what causes it or what you call it, it's nice to look at.
Thanks for your reply. However I'm not so sure. It looks as though some sort of clay could have been used. However, I looked at the actual coin under a microscope, I think it looks more like a crack because it goes under the lettering. As well as the letters are being flushed down the toilet. I found the following photos online but have yet to find a name and don't have the patients to watch the entire mint process to see if maybe it could have gotten stuck in a roller or something. ( *again these photos are not my coins, but what I found online)
I've used the word "chatoyance" to describe the effect of luster for many years (although some argue with my use of the term). It doesn't have anything to do with die polish, however - its all about the metal flow. As the coin is struck, the metal tends to flow radially outward from the center. These flow lines are what we see as luster. However, some coins have basin shapes (the curvature of their fields) which are not uniform. Or, because of the shape or relief of the coins, the metal flows unevenly. On a low relief coin, or a coin with a shallow basin, you'll tend to see a single cartwheel. However, on something like the Mercury reverse (with both a high relief and a high basin), you'll get multiple pinwheels instead of a single cartwheel. You'll notice something similar on the Buffalo nickel as well. As far as I understand your question, @iPen , the effect you are asking about has nothing to do with ghosting. The apparent "ghost" image of the other side appearing occurs late in the life of a die. However, the pinwheel effect occurs throughout the life of the die and is a result of the design of the coin.
