Having run out of 10¢ coins to noodle, and not wanting to start on the 5¢ at this late hour, I had a look at the sack of rejects and thought I'd give the edges a good hard look. I ended up with two questions:
1. Why do a very small percentage of the current obverse exhibit what I'll call the "zipper effect", where the reeding looks to be in two halves, slightly mismatched?
2. Why do some coins seem to have no reeding at all? i don't mean worn, I mean no evidence of reeding ever having been there?
Clearly, its not possible they were minted with plain edges. So this has to be wear. But why is the wear so severe on these coins that the reeding is completely obliterated, even though the faces are no more worn than any other coins?
On closer examination, I was surprised to find that all these coins have cupped rims, rather than the usual squared section. I would surmise that this creates a weaker rim, more susceptible to wear than normal.
But, since they span a range of years, 1966-1989, I'm at a loss to explain how this came about. Perhaps someone with better knowledge of the manufacturing process can shed a little light on this? Are the two observations related? Did something change that replaced one effect with the other?
we usually call the coins with no reeding and rounded rims, dryer coins, for the simple fact that it would take something like that to happen quite a while rolling round and round in a drier etc.
I think I know what your talking about fulvio, well I hope this is what your talking about as I've been thinking the same. Sorry about my usual crappy pic's but here's some 20 cent with the ring around the rim and some 1988 5 cent and if you look really really really hard you can just see very faint reeding
(http://i44.tinypic.com/300qgzd.jpg)
(http://i41.tinypic.com/254zmf6.jpg)
(http://i42.tinypic.com/1z1qqfr.jpg)
(http://i44.tinypic.com/5zplzm.jpg)
Correct, that's exactly what I was talking about, though I'd already discarded any that showed the slightest sign of remaining reeding. Dryer coins.. I love that! :)
So, any clues as to what causes the "zipper" around the rim?
Not really sure sorry but it could be like an up set, if you look at the first pic you'll see that they don't line up and have funny little uniformed marks that only go half way along the reeding that makes it look split..just typical quality control that we now come to expect :winkextra:
I'm trying to remember from the mint tour exactly how the dies are set up. Certainly the collar is a single piece, and no matter how the planchet is struck, it shouldn't end up looking like that. Hmmmm....