What is a "Spark Erosion Counterfeit"?

MrEureka

Somebody, please enlighten us.

ziggy29

http://www.pcgs.com/articles/article1796.chtml

n the spark-erosion process, a model coin (usually genuine) is submersed in an electrolytic bath where the coin faces the counterfeiter's die steel. An electrical current is charged through the coin so that a spark jumps across the shortest gap between the coin and the die, thus etching the coin's design onto the steel die.

After both the obverse and reverse have undergone the electrical current process, the dies are highly polished. This is necessary because once the dies have been etched, they remain somewhat pitted. The polishing generally will clean up the fields, but often the design will retain the pitting, since counterfeiters tend not to polish the main devices. Either they are unable to get down into the design, or for time's sake they choose to leave the design elements alone. In either case, these counterfeits are easy to detect, since their surfaces are glassy smooth-resembling a Proof finish-yet their devices are lumpy (remember, the pitting on the dies becomes raised lumps on the finished product). Because the excessive polishing makes the dies sharp, these counterfeits appear to be extremely well-struck, with knifelike edges and rims.

These counterfeits usually are found on small-type coins such as cents and dimes, and on small-sized patterns such as those for Flying Eagle cents and dimes. PCGS has not encountered them on gold coins.

Dog97

Gee, I know something that MrEureka doesn't!
Basically, electricity is hooked up to a coin and a blank die and sparks arcing between them removes metal from the die thus transfering the design. Easily discernable because it leaves pits in the dies which transfers to the coins struck with it. Also destroys the coin being copied.

MrEureka

Thanks, guys!

How about some pictures?

RKKay

Andy: Next, are you going to ask what a pattern is?

Dog97

For a picture look on page 227 of the PCGS Grading book.

Gemini

Andy when you get the technique perfected see if you can whip me up one of those Central American gold ounce coins.

Leiana

<< <i>Thanks, guys!

How about some pictures? >>



There are some pictures in this article.

-Amanda

numisma

What most articles fail to elaborate upon is the fact that the dies can be used for either stamping dies OR cast molds. I really think that any article out there on this subject over-simplifies the process and the potential danger to collectors. I have seen this process done in person and in great detail.......from start to finish. It can be scary. You will note that in the PCGS article posted by ziggy, they claim that they have not seen spark-erosion counterfeits done in gold. That's because they are often more refined than other spark-erosion counterfiets, or EDM counterfiets, which is the term I use most often. EDM stands for electro-discharge machining. It is an old process. I have seen slabbed gold coins that were created through the EDM process. You would not be able to tell the difference from the real thing.

michael

What is a "Spark Erosion Counterfeit"?

screw those

waht i reqally want to know is the edm counyerfeit

BigE

"enlighten us", who is us?, then I'll tell you---------------------BigE

originalisbest

I don't doubt Dennis for one minute - it can be scary out there! By all means, I'd like to know more about EDM fakes as well.

Dog97

numisma Dennis it does oversimplify it. The VAM book goes into more detail. It describes how a nonconductive fluid is between the dies and the coin being copied for cooling and to wash away the metal residue. The area of the coin that is closest to the dies arcs first then moves to the next closest area working it's way down to the low flat fields. The coin being copied is destroyed in the process and it sometimes takes several coins to transfer the image so that's why you don't see many gold coins made from spark erosion dies.

jimjenson

With the power of computers and 3d cad modeling, EDM fakes will make the example in the article look like childs play. I know for fact that a CNC Agie sinker is capable of surface finished in excess of 6 microns, which would nearly eliminate the necessity for die polishing (say goodbye to the telltale pits). You wouldnt even need an electrode with a neg coin surface in it (as the article mentions), since a series of specifically shaped electrodes and a computer controlling the axis's could generate most any shape captured in your computer model.

link

jimjenson

And heres where the cad models come from. Technology has come a long way since the article on edm fakes was written, or the writer is unaware of just whats out there.

This is not the only vision system out there. I recall seeing them at a trade show 10 years ago. CNC sinkers have been around many years longer.

Heres a system with integrated software. There are several to choose from.
link

Leiana

<< <i>The coin being copied is destroyed in the process >>





-Amanda

dorkkarl

excellent thread, & extraordinarily valuable information

K S

PerryHall

<< <i>Also destroys the coin being copied. >>



Many spark erosion dies were made using modern coins worth only face value in order to produce mint errors such as double struck coins.

Dentuck

Rick Snow article on fake/altered FE/IHc, including spark erosion counterfeits

numisma

<< <i>And heres where the cad models come from. Technology has come a long way since the article on edm fakes was written, or the writer is unaware of just whats out there.
This is not the only vision system out there. I recall seeing them at a trade show 10 years ago. CNC sinkers have been around many years longer.
Heres a system with integrated software. There are several to choose from.
link >>



Jimjenson, I know exactly where you are going with this and you are correct. I have hands on experience with this process as well. A coin can be scanned with a laser at a very tight X-Y grid. The resulting output is an incredibly dense 3D point cloud. This point cloud (really a conglomeration of X-Y-Z points in space) can then be used to make any number of rapid prototypes (molds, dies or the parts themselves). You can also use the data to CNC machine tool steel to make a stamping die, although the machining of such intricate data is not easy. That's why EDM or spark-erosion is more popular. It's Just less time consuming. Also, EDM does not necessarily destroy the host coin. It depends on various factors. It will, however, damage the coin, but you would still have the genuine example after the dies are made.

originalisbest

So with all that said, how are the coin grading services to catch it? If they cannot, then we might be doomed to, say, 1921 Double Eagles that can be made at will? That is, if there's not a microscopic giveaway...?

Regulated

OK Andy, where are you going with this?

jimjenson

Considering this article was written in 2000, the technology being described is from the 60's.

In 2000, the original coin would not have to be used as an electrode. The end results would be considerably better too. I would imagine it would be possible to crush (coin) silver kennedy half into any other half with the same weight blank, providing you had a surface file and access to a decent CNC Sinker EDM to burn the cavities.