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Technology The technology used to produce fakes.

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Old Jan 25, 2004, 08:30 AM   #1
esnible
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Falsifying the appearance of ancient silver

To the naked eye the surface of this Mesembria diobol looked ancient. The loupe showed some corrosion. When examining the coin under the microscope I realized the corrosion was 'growing' on the coin's surface, rather than eating in.

Robert Kokotailo suggested (on the ACFDL email list) that the coin was probably false. His argument was convincing, and was based not on the surface conditions but on the die. If he was correct then the coin demonstrates false corrosion that fooled me.

The 'growths' might indicate splattering of the substance which was applied to give the appearance of artificial surfaces. I have further pictures and discussion at http://www.snible.org/coins/mesembria_fake.html .

If Robert is correct in calling the coin false it might be worthwhile to discuss the surface appearance of this coin. It might also be worthwhile to analyze the growths. Any suggestions for doing the latter?
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Old Jan 26, 2004, 09:52 AM   #2
bruce61813
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Re: Falsifying the appearance of ancient silver

Ed, I have looked at the photos, I have some comments and questions:

[quote]Originally posted by esnible
To the naked eye the surface of this Mesembria diobol looked ancient. The loupe showed some corrosion. When examining the coin under the microscope I realized the corrosion was 'growing' on the coin's surface, rather than eating in.
There are some types of corrosion that are totally surce, the eventual damaage is the the surface "wears down" and becomes smooth. "Self proctecting" metals develope a surface coat that prevents furthers reaction, but these can be worn away. So, the simple fact that there is something on the surface, does not count against it.

Robert Kokotailo suggested (on the ACFDL email list) that the coin was probably false. His argument was convincing, and was based not on the surface conditions but on the die. If he was correct then the coin demonstrates false corrosion that fooled me.

The 'growths' might indicate splattering of the substance which was applied to give the appearance of artificial surfaces. I have further pictures and discussion at http://www.snible.org/coins/mesembria_fake.html .

The "bumps" don't appppear to be material splattered then driven in. These would have distinct indent folds, press something into clay then look at it to see what I am talking about. It appears more likely a casting, where there are small pores in the mold material, these would show as bumps. Also remember the discussion about alloys, and the hard and soft areas. If something is slowly eating away the surface, the "bumps" may be remainders of harder material.

If Robert is correct in calling the coin false it might be worthwhile to discuss the surface appearance of this coin. It might also be worthwhile to analyze the growths. Any suggestions for doing the latter?
It would take a true metalurgist, or an expert in the field of coin metalurgy to say what is happening. You might try the Smithsonian, some of their experts might be able to suggest answers. We need to get a metalurgist to start collecting ancient coins .
I can't say the coin is real or fake, but these are questions that come to mind. Many items have been condemnned by visual observation, that turn out real, and the other way also. Protected coins, found inside a protective item, like a pot or vessel of some type, may be the hardest to deal with beacuse the environmental factors are very different, from the "just buried" coins.

Bruce
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Old Jan 26, 2004, 11:17 AM   #3
esnible
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Bruce-

(My experience with casts is very limited, so my comments are somewhat speculative in nature.)

I think this coin is either genuine or has been sprayed with a metallic-colored glue.

I have a high-resolution picture of a different cast fake with bumps ('pimples') on my web site at http://www.snible.org/coins/cast.html (hi-res picture near the bottom. I'm going to re-shoot that picture from an angle to make the bumps visible.) The bumps on the Mesembria look different. In addition, the other coins from the condemned group shared dies but were not mold mates. Other coins in the same group lacked obvious bumps.

I agree that surface growth doesn't condemn the coins. I originally thought the Mesembria had a genuine but unusual surface condition. After Kokotailo doubted the coins I began to speculate on false bumps. If Kokotailo is wrong then this coin should be put into the 'Coin Surfaces' discussion and a name for this type of legitimate growths found. If Kokotailo is correct then the bumps provide a clue towards current methods of falsifying ancient surfaces.

Examine again the "Obverse and top" picture on the web page showing the rim. That picture makes it look like something was glued to the coin. Can you suggest additional photographs that would help clarify the situation? I am also willing to send this coin for your personal examination.
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Old Jan 26, 2004, 12:14 PM   #4
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I don't quite believe the "glue" theory, but the two sets of coins don't appear to be the same, as to the production methods. Remember that part of the casting is the type of medium used for the mold. If a very fine sand or sand/clay mix was used, the cast might have the appearence of the last pair of coins that you reference, there is some surface reticulation [deep etching] that is apparent, but I do agree that it was cast.
I am just not that knowlegeble in that area. I have sent an e-mail to Dr. Peter Northover, http://www.materials.ox.ac.uk/people...orthover.html,
and referenced this discussion. I don't know if I/we will hear anything from him, but it was worth a try. The Oxford Materials group have been actively working in the metalurgy of ancient metals, not just coins but all types of metals. If we can get an answer, it will help.

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Old Jan 26, 2004, 02:06 PM   #5
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Deja Vu! Robert Kokotailo is surely correct. This is without any doubt in my mind a coin from the Black Sea Hoard group, although neither the obverse nor reverse dies exactly match the previously published examples. To help those who might not recognize the stylistic problems, I will post my Celator article from "way back then" in the forgery articles section on this site. It may take Bill a few days to get it online, but watch for it soon. It does not really surprise me that additional dies exist. The original published dies were not the result of any exhaustive search, they were merely the dies that happened to exist in a group of some 200+ specimens that were sent to Dr. Stanley Flegler for analysis. If you are agreeable Ed, I'll add the photos of these dies to the ones already posted in the gallery here and will add identifying numbers to them. I suspect that there may be a lot more of these little devils lurking about, but no one has really gone looking for all the dies. The die combinations from the group mentioned above are published in my Celator article.

I am following this discussion about surface conditions with great interest. Nobody really did any of this "forensic" analysis when the hoard first appeared. Dr. Flegler's analysis was primarily an examination of the metallic composition, not the method of manufacture and aging.

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Old Jan 26, 2004, 05:54 PM   #6
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When I first started collecting I read Dennis Kroh's speech. He reveals that some fakes are given a false patina while inside a goat! [ http://members.aol.com/kroh/fakes.html ]

In _Modern Counterfeits ... from Bulgaria_ PK&P discuss more convincing techniques of attaching foreign materials to surface of false coins. They say sometimes chemicals are used, sometimes glues, and sometimes mechanically. One new technique is to push the forgeign materials into the surface with high pressure steam.

Wayne's book talks about painted patinas, glued patinas, and potato mold. I've seen painted patinas on fakes, but I don't know what to look for with the glue and mechanically false patinas.

I will be curious to hear any comments from Dr. Northover.

[My excuse for buying a Black Sea fake is that I was at a coin show and did not have access to the Internet to compare pictures.]
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Old Jan 28, 2004, 11:17 AM   #7
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Actually, I would like to get a fake sometime, so that I could see "up close & personal" what makes them tick. Sometimes nothing is better than first hand & in-hand observation. I hope we get some other responses.

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Old Jan 30, 2004, 07:55 AM   #8
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I received a reply from Dr. Peter Northover, and I replied in return with this URL and Eds URL for the mesembria picture/article:

"Dear Bruce,

Thank you for your query. There is probably not too much literature around on the corrosion of ancient coins, mainly because much of the numismatic world seems to like coins cleaned within an inch of their lives. One useful publication, which was directed mainly at conservators having to deal with badly corroded coins from exacavtaion is: Dana Goodburn-Brown and Julie Jones, eds., 1998: Look after the pennies, Archetype Press

It is not often that I get to look at potentially fake coins, a majority of my numismatic work being on excavated material. When I do look at fakes, which tend to be of Celtic gold, I look at the corrosion from the point of view of what I am, a professional metallurgist, and assess whether it is consistent with the likely history of the coin. Suspicions of an artificial corrosion process can then be checked with microanalysis as well as various microscopes.

Your reference to "humps and bumps" is also of interest. Different coining techniques can leave different physical traces on the coin. This is a very neglected area because the metallurgical process of coining seems only to be of research interest to a very small minority. Also, because the people really concerned with the process are tucked away in national mints etc. there is not a widely circulated scientific literature on coining.

Yours,
Peter
--
Dr Peter Northover, Materials Science-Based Archaeology Group,
Department of Materials, University of Oxford
Tel +44 (0)1865 283721; Fax +44 (0)1865 841943 Mobile +44 (0)7785 501745
e-mail peter.northover@materials.ox.ac.uk "
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Old Feb 2, 2004, 10:16 AM   #9
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A reply from Dr. Northover:

"Dear Bruce,

I have looked at the image and discussion and suspect that the surface of the fake is mainly a function of the casting of the blank from which the coin was struck. The corrosion issues may be something of a red herring here.

If somebody is willing to sacrifice a couple of the fakes for destructive analysis we could certainly work out a lot about how they were made. As we provide these services on a commercial basis we would need a little sponsorship - USD 500 would almost certainly cover it. If we came up with clear-cut result, as I believe we would, you would then be able to interpret a lot more coins.

Yours,
Peter"
So we have some options.

Bruce
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Old Feb 2, 2004, 08:14 PM   #10
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Fortunately, destructive analysis of these coin has been conducted. The results are included in a report from Dr. Stanley Flegler of Michigan State University to the IAPN. A copy of that report was published in The Celator and will soon be posted in the articles section of this web site. The results of Dr. Flegler's tests were surely accurate, it is the conclusion he reached that was controversial.

Wayne
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