Silvering of denars and its counterfeitsToday in the
German Forum a member has posted a dissertation about the
silvering of denars and their
counterfeits. I think it is so important that I should mentioned it here.
Gunther
Kraft, Chemisch-Analytische Charakterisierung römischer Silbermünzen
Dissertation: TU Darmstadt, Fachbereich Material- und Geowissenschaften, 2005
You can find it under the following link:
http://elib.tu-darmstadt.de/diss/000609/Format PDF 1.3 , readable with Acrobat Reader 4.0
Abstract:
In the context of this
work 35
Roman silver coins from approx. 215 BC to approx. 330 AD were investigated. These were mainly
contemporary forgeries being emitted by counterfeiters as alleged pure silver coins with the aim to become wealthy. Earliest issues of officially
silvered coins are known as of the late successors of the denar (from approx. 250 AD) which mostly, with
rare exceptions, are not distinguishable from unofficial pieces. The chronological structure of the dissertation allows a review of the origin and development of
silvering techniques in the course of time. During a period of approx. 500 years the enhancement of
silvering techniques precipitated a decline of the silver coatings from approx. 100 m to 1 m. The unknown but lively discussed manufacturing process of the
Serrati was uncovered carrying out a thorough analytical investigation of this notched shape of the
republican denar. Thus especially forged
Serrati were of interest as their production required exceptional effort and skills. The
applied analytical methods were High Resolution Scanning Electron Microscopy (HRSEM), Electron Beam Micro Analysis (EPMA) and Secondary Ion Mass Spectrometry (SIMS). Especially thin silver layers of
contemporary forgeries and those of later officially
silvered issues are often in bad condition and can only be identified as silver coins due to their embossed figures and
symbols. The distribution of the silver permits the characterisation of such coins, as existence and appearance on the surface already provide an indication of the coin production technique. Element distribution images of
complete coin surfaces can be measured by increasing step sizes between the measurement points. These distribution images give evidence of suitable positions for SIMS-measurements which allow to obtain the silver layer thicknesses of the coins. The detected thickness values also indicate the
silvering method used. By combining the respective results it was possible to identify the production method which
had been
applied to silver a coin.
Methods:
1. Plating (Fourees)
Thickness of the silver layer ca 100 micrometer
not in the later Empire because of its high silver demand
2. Amalgamation with Hg
for gold only, core must be Ag
Thickness 20 micrometer, high Hg content (to 10%)
3. Treatment with acids ('Weißsieden' = white boiling?)
needs an Ag content of more than 15-20%!
Thickness 5-10 micrometer
4. Later technologies (since midth of the 3rd century)
a) Melt of AgCl, or other Ag ions
Thickness 1-5 micrometer
not seen until now!
b) Moesta, Cope:
Alloy of Cu, Ag (2-5%), Pb (5-10%), treated with acids
Thickness some micrometer
His work shows that in the beginning the counterfeited denars were
plated whereas in
the late Empire the methods described by Moesta and Cope were used.
Best regards
