Physico-Chemical Unmasking of Sicilian Bronze Fakes

[Lloyd Taylor]

With thanks to CFDL for pointing the way to this article... Download:   http://www.maajournal.com/Mondio_9.2.pdf

This article may be of interest to those seriously pursuing fakes:
Ancient Coins and their Modern Fakes: an Attempt of Physico-Chemical Unmasking.
A.M. Mezzasalma, G. Mondio, T. Serafino

In Mediterranean Archaeology and Archaeometry, Vol. 9, No. 2, pp. 15‐28 

Abstract
As a consequence of police operations, a huge quantity of perfect imitations of ancient coins, realized by a sicilian forger, has been recently found. Such fakes have been realized by the lost wax casting technique and reproduce coins issued by different authorities in different historical epochs. In order to overcome the obvious subjectivity of the traditional (autoptical) numismatic analysis, which sometime provides contrasting interpretations, the fakes have been analysed by Scanning Electron Microscopy (SEM) and Energy Dispersed X Ray Fluorescence (EDXRF). The results obtained have given information on the microstructure, the homogeneity and the elemental composition of the alloys used by the forger. Furthermore, evident traces of the chemical treatment utilized for the artificial ageing of the coins have been found. Due to the presumable and dangerous large diffusion of these sicilian fakes in the international market, the results of such analyses may certainly be of noticeable interest for Numismatics and forensic applications as well, representing a set of proofs to be used in the unmasking of analogous counterfeiting cases.

Keywords: Scanning Electron Microscopy (SEM); Energy Dispersed X-Ray Fluorescence (EDXRF); Coin Fakes; Numismatics.

[James Anderson]

Fakes produced by this method should all be exactly the same, "perfect imitations" and therefore should be easily recognizable.

[Lloyd Taylor]

Fakes produced by this method should all be exactly the same, "perfect imitations" and therefore should be easily recognizable.

Not quite...the lost wax techniques permits individual reshaping of every flan if desired by the faker.  Then there is the question of post-cast stressing, wear and patination.  Quite different products (each a "perfect imitation" of something different) can be achieved from the same master mold with very little incremental effort.  Unfortunately, the article doesn't detail the "enormous quantity of numismatic material" seized by police, but it does suggest that the "quality" (and thus appearance) varies. I very much doubt that the forgers produced sacks of identical coins given the apparent scale of the operation.  Were it to be the case the "physico-chemical unmasking" would hardly be a relevant, or necessary adjunct to the inquiry and proceedings.

[driekus]

If I remember correctly x-ray fluorescence should give you an indication as to the chemical composition. This could be used in two ways, the first you could detect any surface treatments. The second would be to detect the composition of the metal surface itself. Ancient bronze was a crude mixture of elements, something that is near impossible to replicate in a modern environment. It would also be region and mine specific. I would presume this would only be replicable if you mined your own copper from a roman mine using ancient roman techniques.
Thanks for the article, it was a good read.

[Snegovik]

X-ray fluorescence will detect the composition of the whole sample, not just the surface. It is very difficult to distinguish between the surface and the body by this method. 

[daverino]

X-ray fluorescence will detect the composition of the whole sample, not just the surface. It is very difficult to distinguish between the surface and the body by this method. 

Unfortunately, not the case. XRF will only detect the surface composition and these authors explain that first they analyzed the composition of the patina, and then the bulk concentration using a cross-sectional cut of the fake coins.

It would be useful to find a non-destructive method of analyzing bulk metals. Most of these fake "bronzes" show very little variation in their components (Cu,Sn,Pb) even though of different eras.

[Snegovik]

I can only reiterate that I am skeptical about quantitative results reported in this paper. 'Surface concentration' is meaningless - the depth of X-ray penetration into the sample depends on the brilliance of the source. I also expect that structural features might vary depending on the conditions of preservation and methods of treatment. The only result is that the composition of ancient alloys is different from modern ones. That could have been predicted. The information on the amount of contaminants in the metal used by the forger is useful for spotting his other forgeries provided you have access to the necessary equipment.

[daverino]

The general problem with these studies is that the research is aimed more at training students in the use of modern analytical methods( so that they can get jobs} than on developing a method for identifying forgeries. It  seems to me that the forgers might be vulnerable on two points

1) That they use modern "clean" metals which don't have the numerous trace contaminants that the ancient sources had.

2) That forgers are inclined to be consistent in their metal alloy composition. There was likely no set method for making ancient alloys and so the percentages of metals would vary from batch to batch.

Detecting trace elements requires sophisticated instruments (at best) and/or destructive procedures (at worst). On the other hand I have found looking at the electrical conductivity of 3rd century Roman antoniniani (composed of Ag, Cu, Sn and Pb) to be somewhat useful in detecting fakes. Based on my limited tests, I would be extremely skeptical of a batch of bronzes all having the same conductivity (which is to say, the same tin content) or antoniniani having a very high conductivity (indicating very pure copper).

An exception to the latter rule may be copper coins from the Gallic mints.

[driekus]

I didnt think x-ray fluorescence was destructive unless you took cross sections.
Snegovik, I can see where you are coming from, but Im hoping the authors will start a more detailed study on a wider selection of roman coins. I dont know whether this will lead anywhere but I think its worth finding out.