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Authenticity Distinguishing between genuine and fake objects.

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Old Jan 20, 2004, 09:34 AM   #16
bruce61813
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We should assemble a ollection of photographs first, I would recommend closeups of specific area to illusltrate tha "term" we want to define. Post in semi-private area, defined the terms and illustrations and the post.
Silver coins, especially solid or very low copper content coins , may exhibit crystallization, that would require a microphotograph to really show the change [anyone have a broken coin?]. The concept of porous is more in the realm of bronze and brass coinage, as tinn and zinc are subject to leaching. Surface etching, may occur on any coin and will show up in many forms - from finger prints to Ed's hemi. Generally it is a surface phenomenon, where softer areas are removed, leaving the harder areas exposed. Damascas steel items are the best known examples.

Bruce
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Old Jan 20, 2004, 10:00 AM   #17
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Doug, your trihemiobol is very nice. (The Neapolis hemidrachm above is my nicest.)

I wouldn't attempt to 'correct' the professional catalogers. They are far more experienced than I! Their descriptions are at the correct level of specificity for buying and selling coins. I think their descriptions are too vague for discussing the authenticity of coins.

I started this discussion because the first coin in the thread, the Apollonia Pontika, was thought by a dealer to be false. I thought it was genuine and 'crystallized'. We didn't couldn't agree if the coin was 'crystallized.' Vocabulary clashes are a barrier to genteel discussion of authenticity.

I sometimes take coins to shows and ask the opinion of dealers. I get answers like 'it has ancient surfaces'. I don't know what that means!

Many books say one should inspect coins under the binocular microscope to look for problems. That's true, but how? A book on using a microscope for biology talks about staining, what is a cell wall, how thick the wall should be for a plant cell vs. an animal cell, etc. Through this ancients.info topic I'm hoping to explore what a chapter on Microscopy in an book on Ancient Coin Authentication would contain.


I attended a talk last weekend by Dr. Ursula Kampmann on forgery detection. She said a 15x loupe is necessary for detecting the best casts. I bought a 10x loupe three years ago! I looked at pictures online of casting bubbles and thought they were always big, so I got the 10x loupe. Now I discover I have been 5x too short for years.

Above I link to a *genuine* coin from a CNG auction which has casting bubbles. If someone questioned that coin on a list I wouldn't want to debate folks who 'know' all cast coins have 'Toronto-sized' bubbles. I want to raise the level of discourse and one way is to have a visual glossary of the surface features of coins.
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Old Jan 20, 2004, 11:04 AM   #18
wgsant
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Doug, Ed, et al.

I think this discussion is perfectly appropriate in a Forgery thread, even though we are talking about genuine coins at the moment. As Ed has pointed out, it is essential to understand the nature of genuine coins before we can understand and talk intelligently about fakes. In this area of numismatics, there is very little concensus and we may well establish our own criteria here to develop a terminology that we can agree on. It is a very subjective area, and one that has both "scientific" and "street" language being applied by a great number of people with varying perceptions and degrees of accuracy (myself included). I'm sure that we could get Bill Puetz to add a gallery section for "Glossary Terms" and as we reach a concensus here we could upload representative images to that gallery. If you all think that is worthwhile, I'll talk to Bill about it.

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Old Jan 21, 2004, 08:12 AM   #19
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another image

Wayne;

While I don't disagree that studying real coins is the best thing to learn about fakes, I do believe a separate section for the proposed photo collection would be worthwhile. Also, I seem to fail to understand how to place images on my post using the Attach File utility. I can link to an image on my web space but attaching JPG's doesn't seem to work. It would seem that our image collection would be better copied to the Forum space rather than linked to individual sites (which could change leaving bad links). Opinion?

I see now. The image does not appear on the Preview but is there with the posted note. This one shows something I considered interesting on the reverse top. What is shown and what does it say about the coin?
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Old Jan 21, 2004, 08:49 AM   #20
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Doug, the "intersting" feature looks like embedded brass or gold [since this is "cleaned" , I can't tell which. The brass would eventually turn green, but gold would stay yellow, although my guess is gold]. I say embedded, not part of the coin alloy [ I am assuming pure or nearly pure silver] as you would not see distinct areas. But if it were tiny pieces picked up in the die or flan, then sturk, it would embed in the coins fabric, and fuse during cooling.

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Old Jan 21, 2004, 09:35 PM   #21
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It looks to me like an accretion from proximity to another metal (perhaps a coin) by electrolysis while in ground. This deposit apparently did not come off in the cleaning. If so, this could be an argument that the coin is probably of ancient origin (although there is little doubt anyway in this case).

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Old Jan 23, 2004, 08:43 PM   #22
esnible
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Bruce, would you say this coin also exhibits 'surface etching'?

The holed Neapolis gorgon has an etched surface that resembles cloth. Under the microscope that coin looks dark between a weave of silver.

This new coin, an Apollonia Pontika gorgon, has a surface that resembles snakeskin. There are no long silvery lines -- the pattern is more like dried, cracked mud.

When I saw the auction picture (inset) I was nervous because I'd never seen a published Apollonia Pontika where the snakes came out of the cheek, like whiskers. Three or four from this die appeared on eBay over the course of six months. Seeing the surface pattern was reassuring.
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Old Jan 24, 2004, 12:02 PM   #23
bruce61813
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Ed, e al,
Looking at the picture of your coin I would have to say that it is the same type process. Different alloys of metal will displat dfferent patterns, and the chemistry that eats into the coin surface will change things also. It is similar to sand-blasting a piece of wood. The hardest grain will remain, almost intact, the softer will be eaten away. It is largely a surfave effect, and does not go deeply into the coin fabric. Deep damage is more oxidation, or errosion, like rust in steel. Generally suface etching is the mildest damage to coins.
The biggest difference is that this is more often seen in silver coins, possibly electrum too, The silver has some copper, maybe a maximum of 10% for strength, even native [natural] silver has some impurities, and I believe copper is found mixed in silver ores. Allow for a few parts of a softer metal in the silver, and you have to think on a molecular level, the silver-copper alloy may be harder than the pure of either metal, and the chemical attack will slowly eat away the softer portions. Also the effects of the coin being struck change the coin surface. Striking the flan also hardens it, many soft repeated hammer strikes will harden gold
so much that a jeweler cannot work on a ring without annealing it [heating the ring to a near red condition and letting it slowly cool].

I am getting long winded, hope it makes sense. Great examples.

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Old Jan 24, 2004, 02:14 PM   #24
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Bruce, your example of sand-blasting a piece of wood is very good. Do not worry that your replies are long-winded. This thread keeps going idle and I keep returning to it because I am so interested. Now let me be long-winded.

I went to the wood-working glossary at http://www.wood-handbook.com/wood-ha...glossary-5-f-g and found these terms for describing wood grain: close-grained (=fine-grained), coarse-grained, cross-grained, curly-grained, diagonal-grained, edge-grained (=quartersawn), end-grained, fiddleback-grained, flat-grained (=flat-sawn, =plainsawn, =side-grained, =splash-grained), interlocked-grained, open-grained, spiral-grained, straight-grained, vertical-grained, wavy-grained.

(Also think of the pattern on burl, and what knot-holes do to lesser boards.)

I took wood shop in high school and only learned 1/4 of these words. All these words are used in specialized woodworking. The definitions of these terms relate to how the circular rings are revealed on the board, which depends on where in the log the board was cut from.

Similarly, to understand coin surfaces, we must understand about how metals mix. Let me summarize what I've learned:

Coin metal can be well-mixed or poorly mixed. Poorly-mixed coins have week 'streaks' like the fudge-ripple in ice cream. The streaks can fracture allowing the surface to chip away. Well-mixed coins have honeycombs/webs (?) of softer metal. 'Surface etching' is evidence of good mixing and a harsh environment which dissolved softer metal. The etched grain patterns and grain sizes have not been named by numismatists.

Some coins develop real crystals, especially on the inside. This looks something tiny sparkling pebbles, and something like a geode stone. Wayne's modern replica has crystals on the outside, yet it is not ancient.

Now that I share a basic vocabulary with Wayne and Bruce and Doug, let me start asking about fakes.

In 'Recent Black Sea Hoard discovered to be fake' Kerry Wetterstrom says 'on die ... #2, it appears that 'corrosion' was cut or etched directly into the die as every example we have shows the exact same 'corrosion' in the same area on every coin....' One can't just etch away the die, as that would produce raised patterns on the coin which would look like signs of die rust. If I understand what etching means, the die must have a raised area which would produce pseudo 'etched corrosion' on the coin, yes?

In Classical Deception, Wayne says that 'Costodoulos' introduced 'artificial corrosion and crystallization.' Did that crystallization look like sparkling pebbles within cracks, as on the Rosa trial strike? Was the 'artificial corrosion' artificial surface etching, artificial porosity, or something else?
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Old Jan 24, 2004, 07:51 PM   #25
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Ed;

This thread is indeed becoming interesting and thanks for continuing to prod it along. I'm as guilty as the next person about using terms that sort or "come with the territory". When I talk about crystallization, I have a very specific idea in my head. But, when I try to explain that idea in an intelligent way to intelligent people I find that my own knowledge falls a little short. This thread is causing me to think more seriously about the terms that I use and why I use them.

As for the modern Rosa copy with crystallization, that crystallization is not on the "outside" of the coin. The photo that I posted is taken so that it looks into one of the broad flan cracks and the crystallization visible is actually the interior of the coin. The surface of the coin (I use the term "coin" loosely here) is smooth and free of any sign of crystallization.

My comment about the introduction of crystallization and artificial corrosion was based on the observations of others and I can't say in truth exactly what they looked like. The few "Costodoulos" fakes that I have seen were not encrusted in any way because frankly they were expensive coins and one would naturally expect that they had been professionally cleaned before being offered for sale. As for corrosion being purposely introduced in the die, I would guess that the kind of surface modulation that one often sees in struck coins can be replicated in a die to enhance the realism of the end product. This may be corrosion or simply an uneven texture about the surfaces. Few genuine struck coins have really mirror surfaces after 2,000 years of aging (certain gold coins perhaps excepted).

I understand your point about "engraved" corrosion appearing in relief on the coin produced from a die altered this way. It would not be feasible (nor necessary) to engrave a "pit" into a die. A pit can easily be added after the coin is struck. It would be feasible, however, to roughen the surface in a way that replicated "rusty dies" or localized corrosion.

Ed, I'm sending you a broken Greek drachm that is badly crystallized internally. Maybe you can cut it in half and get some good photos for us.



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Old Jan 24, 2004, 07:57 PM   #26
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I just noticed that Bill has added the Gallery section for "Visual Glossary" I will be happy to entertain nominations for submission to this category and if we have a consensus here we can start to build a useful glossary. Does anyone want to pick a term and a good illustration for openers? You can post the images you wish to nominate in your own member gallery and I or one of the other moderators will move them to the Glossary section when concensus is established.

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Old Jan 25, 2004, 11:24 AM   #27
bruce61813
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Ed, you have the idea
"Coin metal can be well-mixed or poorly mixed. Poorly-mixed coins have week 'streaks' like the fudge-ripple in ice cream. The streaks can fracture allowing the surface to chip away. Well-mixed coins have honeycombs/webs (?) of softer metal. 'Surface etching' is evidence of good mixing and a harsh environment which dissolved softer metal. The etched grain patterns and grain sizes have not been named by numismatists."

Think of the "good" mix as 1 tin atom with 10 copper atoms evenly surrounding it in a sphere, stack millions of these together, using a tin atom to attach the spheres. There are spaces between the spheres and their arrangement is what determines the "crystal" or latice structure [in the alloy case]. There are limits as to how much of one metal may be mixed with another, for bronze 1 tin to 10 copper is the ideal, other ratios produce less strong alloy. The same holds for silver, usually there are some impurities, copper is introduced for durability in coins, again the percentage changes the mechanical properties. So if you are running out of funds, just add 2 or 3 three % more copper to your silver, and you have a larger supply of coins! But they will not be as good, both value or mechanically [they are softer] and in some cases they may become brittle.

"Some coins develop real crystals, especially on the inside. This looks something tiny sparkling pebbles, and something like a geode stone. Wayne's modern replica has crystals on the outside, yet it is not ancient."

Are the crystals part of the metal fabric, or did they grow in the cracks by chemical deposition. I found a micro geode on the face of a large uncleaned bronze. It was about 5 mm, but it shattered when I tried to open it a little more. I wanted it intact, but viewable. Beautifully hollow with a lining of bright crystals, hence the question. As I said before, metal will become "crystalline", but you have to check the definitions that are used by metallugists.

"In 'Recent Black Sea Hoard discovered to be fake' Kerry Wetterstrom says 'on die ... #2, it appears that 'corrosion' was cut or etched directly into the die as every example we have shows the exact same 'corrosion' in the same area on every coin....' One can't just etch away the die, as that would produce raised patterns on the coin which would look like signs of die rust. If I understand what etching means, the die must have a raised area which would produce pseudo 'etched corrosion' on the coin, yes?"

You are correct, and if it is eteched into the die, the same patterns wold be in the same areas, not random, like the examples you have shown.

"In Classical Deception, Wayne says that 'Costodoulos' introduced 'artificial corrosion and crystallization.' Did that crystallization look like sparkling pebbles within cracks, as on the Rosa trial strike? Was the 'artificial corrosion' artificial surface etching, artificial porosity, or something else? "

Artificial corrosion, the same as naturl, only accelerated, can be accomplished, but I have not had time to think about this, or study it. ths discussion id intersting and I hope it continues. There is much that can be condensed and "published" for others.

Bruce
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