I have seen several Roosevelt dimes with radiating lines, look like spokes, from the center out. Does anyone know what causes it? A sample is attached.
The metal at the center of each planchet moves outward toward the collar when struck, and much like runoff carved the Rio Grande over the ages, that movement erodes the dies a little bit more with each strike. Some coin designs leave distinctly radial flow lines, while others leave patterns which have a bit more of a swirling character, and are not quite so easily identified with.
@cpm9ball @ToughCOINS Thanks to all of you. I have been seeing this effect but had no idea where it came from.
Exactly! It's very common on ancient coins, such as these. Click on them to see the phenomenon in higher magnification: Faustina Sr, AD 138-141 Roman AR denarius, 3.83 g, 18.2 mm, 5 h. Rome, AD 150/151. Obv: DIVA FAVSTINA, draped bust, right. Rev: AETERNITAS, Fortuna standing left, holding globe and rudder. Refs: RIC 348a; BMCRE 360 ff; Cohen 6; RCV 4577. Notes: Overstruck on a previously issued coin; undertype not identifiable. Faustina II under Marcus Aurelius, AD 161-175 Roman AR denarius; 2.60 g, 17 mm Rome, AD 161-175 Obv: FAVSTINA AVGVSTA, draped bust right Rev: LAETITIA, Laetitia standing left, holding wreath and scepter Refs: RIC 700; BMCRE --; Cohen 147; RCV 5258 var; CRE 197.
I know that most everything anyone can read says that. But actually, it moves in the opposite direction, from the outer edges towards the center - not away from the center. Think about it for a second, before a planchet is struck it's basically flat. And rim is upset so there will be enough metal there to form the rim. But where is the largest device on most coins ? Where does most of the metal from the planchet have to flow to form that device ? The largest device is almost almost always in the center of the coin. This dictates that most of the metal therefore has to flow from the outer areas of the planchet into the center - otherwise that device could never even be formed. But you are correct in everything else you said. The lines that we see are formed by the metal repeatedly flowing across the die thus creating die wear.
This is an interesting point and I wonder how well it applies to ancient coins, whose flans were not machine-made nor always flat, although they were probably flat-ish. Nor were the coins struck in a collar, so there is a fair amount of outward spread of metal. Some "flow" must be towards the edges and some must be towards the devices (as you said, usually the central part of the coin).
According to the explanation by Mr. Wexler, the die is cone-shaped which would cause metal to flow to the outer edges. (See Paragraph 6 and images below) http://doubleddie.com/58201.html Chris
Ask yourself a simple question Chris - where is most of the metal once a coin has been struck ? The vast majority of it is in one place - the center of the coin. Now if that's the case, and it definitely is - it sure didn't get there by flowing outwards. If you like, you can analyze the laws of physics, they say the same thing. But what I just said above is simple common sense. And if dies are cone shaped, then why aren't coins cone shaped ?
You could also ask yourself another question Chris - where does the metal that forms the central devices come from - what areas of the planchets ? Again, there's only one answer, it comes from the fields. And where are the fields in relation to the central devices ? They are outside the central devices, closer to the rim. So rather obviously that metal that was in the fields area sure didn't flow outwards to get to the middle.
Here is microscopic evidence of this on a proof coin. The rim of the coin is along the bottom of the image, and die polish lines are evident going from bottom left to top right. But look at the streak perpendicular to these die polish lines. In particular, notice the shape: it has a thin tail and a thick head, meaning it accelerated and then decelerated towards the center of the coin. This is the same shape that a liquid makes when it decelerates upon hitting a wall. I admit I was a doubter until I started playing around with a microscope. Here is an image of the entire coin. The die polish lines are evident as diagonal lines in the field. Here are the metal flow lines on a BU Morgan dollar, which attain this structure after many thousands of strikes. The OP’s coin has massive die erosion structures due to having struck many more coing than this die at this point in its life.
