Honest Question: What causes these deep flow lines? (UNC 1976 P Ike T2)

The link I gave in post#36, is to a paper by someone who did an FE analysis of a coin being struck. He did it for the Portuguese mint I think. Google the author (Paulo Alexandrino) and you'll find another paper where he presents results of a study he did that at least references metal flow (unfortunately it costs $50 to download, so I didn't).

Now I know enough about non-linear, large deformation, finite element analysis to recognize that it is entirely feasible to model very accurately the transformation of a planchet to a coin. LS-DYNA for instance is (or used to be) the go to analysis software to model cold form metal pressing, etc. The minting process involves much higher strain rates than cold pressing, but there is plenty of available data to accurately model the constiutive properties of different metals at these strain rates. The number of elements required to model the intricate details of a coin's fields and devices is huge but entirely within the processor power of common high end PC's.

Blah blah blah

 

Log in or Sign up to hide this ad.

This is from http://www.error-ref.com/
PART IV. Die Errors:
Die Deterioration / Deformation errors:
Die Deterioration Doubling
Definition: Die deterioration (die wear, die fatigue) sometimes produces discernible doubling of affected design elements. We call this die deterioration doubling (DDD). Its appearance is highly variable. It is often raised but can sometimes be incuse. Incuse DDD is most often seen on copper-plated zinc cents, but does occasionally appear in other issues. Die deterioration doubling may completely surround an affected design element (like a number or letter) or may be restricted to one side.

The images below shows die deterioration doubling on a 1955 Lincoln (raised), Jefferson nickel (raised) and 1989 Lincoln (incuse).





As to why it causes it...I honestly don't know.

 

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.

 

well, until we have an explaination for why it happens, I refuse to believe it exists.

 

If everyone would slow down and read. It's all here in English and in Black and White : Wexler's Coins and Die Varieties (doubleddie.com)





Die deterioration doubling is another form of common, worthless doubling found on U.S. coinage. Like mechanical doubling, it is frequently mistaken for the doubling that is seen on genuine doubled dies. Unlike mechanical doubling which is formed while the coin is being struck, die deterioration doubling is actually on the die itself. That is the one thing that it does have in common with genuine doubled die doubling. Die deterioration doubling results when the dies used to strike coins are kept in use for too long a period of time.

As a die strikes coins, the impact of the die on the planchet forces the planchet metal into the cavities of the die to form the design that we see on the coins. Gradually, over a period of time, the flowing of the planchet metal into the cavities of the die will cause the surface of the die to erode much like a constant flow of water over an area of land will eventually cause the land to erode.

Since the metal is flowing into the cavities of the die which form the design elements on the coin such as the letters or the bust, that is where the greatest stress and thus the greatest erosion will occur. This erosion of the die's surface will begin to form depressed areas around the letters and other design elements. These depressed or "incuse" areas on the die will form raised images on the struck coins. Since these additional raised areas are right around the letters and other design elements, they give the appearance of doubling to those design elements.

 

I need pictures to prove it of dies doing this

 

I don't understand. The two posts above your "I don't believe it exists" show brilliantly clear pictures of it. Or do you want a time-lapse video of a single die changing over tens of thousands of strikes? If so, you're going to need a budget.

 

Today I learned that sometimes when a dog eats your homework, it retains the information.

 

It just shows doubling. Not the deteriation of dies over time and their effect on minted coins.

 

This is, of course, quite true. It is why Full Steps, Full Band Lines, and Full Bell Lines command a premium. But I am not sure it fully explains the flow in ancient coins, as pictured earlier in the thread. These were not generally struck with flat planchets in a collar, but with rounded, even spherical planchets with unlimited outward flow. If there is nothing to restrain the outward flow, there is nothing to create a force to fill the inner designs, like having a 360 degree cud. Yet the inner designs are often the most defined parts of the coin. The flow is still outward, as is obvious from the wear lines around the letters, but the rounded planchets would have had to have flowed at least simultaneously into those high relief portraits or it never would have made it.

 

No, the flow obviously was not upwards from a thinner planchet. I'm just saying it could not have flowed outward first then upward, because without collars there would be little force to push it up into the central features. I'm certainly no expert, only repeating what I have read (and can't remember exactly where) that they used, at least early on, round or rounded planchets. But I do have a few lower quality ancient coins, and most of them, especially the earlier ones, seem to show this. Here is one from Lydia, around 550 BC. The reverse is a punch, not a separate die. It would have been the "hammer" and the obverse the "anvil." The details seem to fade toward the edges while the metal "puffs out and up" on the edges of the reverse.


Likewise, with this early Miletos, with no collar it is hard to see how flow would have been from the edge to the high relief lion.


It is also noticeable on this Alexander III (I can't id it, but I presume posthumous), especially on the reverse. The high relief of the obverse does not lower the relief on the reverse central devices, but it does toward the edges.