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V13 2010 INDEX       E-SYLUM ARCHIVE

The E-Sylum: Volume 13, Number 21, May 23, 2010, Article 20

NUMISMATIC VOCABULARY TERM: WIRE EDGE

Dick Johnson submitted this amusing and educational item on another numismatic vocabulary term - "wire edge". -Editor

Good morning class. Today we study -- writing on the blackboard
W - I - R - E       E - D - G - E -- wire edge. Who can tell us what is a wire edge?

Ronald Know-it-all: "Metal squeezed out between a die and a collar. It's like a wire."

That's part right. Where do we find wire edges?

Sidney Wise-mouth: "In coin shops."

Ronald: "On proof coins."

Correct. Can you find wire edges on nonproof coins?

Silence. Bewildered facial expressions on class members.

Wire edges can be found on all kinds of coins. It is more evident on proof coins because the pressman is attempting to completely fill every crevice of both dies and, if it is a reeded coin, every crevice of the collar. Remember the obverse and reverse dies enter inside the collar. The collar is a big heavy disc with an aperture in the center that is the exact diameter of the coin you wish to strike. If the coin is to have reeding -- it has the ridges and indentations, these are called knurls and flutes -- on the inside wall of the hole, the aperture. If the coin is to have a plain edge, the wall of the collar aperture is plain.

The dies enter that aperture and smash into the blank. Of course the dies are hard, the blank is softer metal. As the dies drive into the metal of the blank it forces the metal of the blank to flow into every crevice it can. The term for that movement of metal is called SURFACE DISPLACEMENT. Remember: surface displacement.

Ronald: "Is that term going to be on the test?"

It may very well be. It is that important. To continue. Metal from the mass of the blank flows towards the greatest cavities in the dies. What is the greatest cavity on a die?

Sidney: "The eye of the portrait."

No. The die is negative. The greatest cavity in the die is the high point on the coin, generally somewhere on the device. Metal flows towards and fills all the cavities in the die -- device, lettering, stars, whatever -- any raised relief on a coin is a cavity in the die. Metal fills all these cavities at the instant the coin is struck. It also fills the indentations of the reeding in the collar. Now what happens if there is even more metal and all the cavities are completely filled?

Ronald: "It squeezes out. Between the die and the collar."

Right. That is the only place for it to go. There are several reasons for this -- either an overweight blank, with too much mass of metal, or too high a pressure setting on the press. A pressman can reduce the pressure slightly. Or replace the supply of blanks with proper weight blanks. If the pressman continues the press run, this will greatly wear the collar and the rim of the die. Ultimately the rim of the die may break away or a collar may crack. If the rim breaks away from the die what does that cause on all those coins?

Entire class: "Cuds!"

What a pressman attempts to do is strike coins that are fully struck up, fills all the cavities, including the high points. He also attempts to have a flat rim all around the coin and the metal flow to form a perfect 90-degree angle where the rim meets the edge, all around the coin. There is a name for that point, the "rim-edge juncture." Write that down. That will be on the test. Rim-hyphen-edge juncture.

There are several names for that squeezed-out metal. Metalworkers call it FLASH, a small amount of excess metal is called a FIN, when it has to be removed it is called a BURR. American numismatists called it a WIRE EDGE. British numismatists call it a KNIFE EDGE or KNIFE RIM. American and British pressmen are not the only ones who have trouble wire edge anomalies. It can happen to any pressman. But one nationality of pressmen are so good you will almost never find a wire edge on their coins.

German coining technology is so good at every step. They can refine precious metal to .99999 -- called "five-nines." They can blank to a super exact thickness and diameter blank. With a proper weight blank, they seldom experience any coining flash -- no fins, no burrs, no wire edges. Also German-made presses are very exacting. They can control pressure settings to finite exactitude. I have never seen a German coin with a wire edge.

Class, you only need to remember this about wire edges. They are caused by sloppy presswork, too high a pressure or overweight blanks. Also remember the terms surface displacement and rim-edge juncture.

Class dismissed.

Dick Johnson used this term once before in The E-Sylum, in a long article on March 1, 2009. The term appeared near the end of the article. -Editor

To read the earlier E-Sylum article, see: MORE ON THAT COIN TONING EFFECT: NEGATIVE SHADOW AND SURFACE DISPLACEMENT (www.coinbooks.org/esylum_v12n09a13.html)

Wayne Homren, Editor

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