Exciting Brass Contemporary Forgery 1726 Ecu

Actually silvering is present on your pieces its those darkened areas in/around the motifs. Mercuric silvering as in your piece sometimes is worn away but normally a high end benchtop model can pickup Hg levels down to 0.1%. Mercuric silvering depending on the circumstances can darken as it has on your piece. Its difficult to detect Hg even with a $20K Oxford hand held XRF analyzer. Mercury becomes inert in these situations on the surface based on the mercuric compounds it forms- also no problem handling these without cotton gloves. JPL.

The 1783Q that is shown has no edge lettering.
You can see the remnants of silvering in certain places.

L. Beck on her paper on - Counterfeit coinage of the Holy Roman Empire in the 16th Century: silvering process and archaeo-metallurgical replications discusses the mercuric silvering layer being actually THREE distinct layers. An inner copper core/the MIDDLE mercuric silver layer and the outer copper core. Sometimes with copper reacting with sulfides or chlorides can produce this darken effect I discussed with this coin - not ALL mercuric silvering is silver looking as in the other example. See her discussion where the majority of the coins silvered with mercury were struck in Palatinate whereas those with pure silver come from the city of St. Gallenin Switzerland. The mercuric silvering process in general is universal in its technique.

The examination of the coins has shown two main types of silver plating which can be distinguished by the presence or absence of mercury. In case of mercury detection, microanalysis on cross-section clearly shows the
presence of silver and mercury in the same layer (Fig.
1a). This plating layer is between two copper-rich phases, the inner layer is the corroded copper core of the coin and the external layer is composed of copper corrosion products. The presence of silver and mercury in the same layer is non-destructively confirmed by RBS(Fig. 1b). The typical thickness of this plating layer is between 5 and 10 µm.
When mercury is absent, the silvered layer is very thin(1 - 2 µm) and generally less preserved (Fig. 2).

Mercury silvering

The silver and mercury contents of the amalgam silvered
coins were measured on the surface of the coins, and on the cross sections for two coin fragments (numbers
15-15 and 16-5). The results are presented in Table 1.Except for the coin from the city of Strasbourg, the mercury content of the plating is between 25 and 51 %. For
each coin, the result is a mean of at least 7 surface analyses and the dispersion of the data is due to the
heterogeneity of the alloy. On the cross-section of the fragments, we have observed that the plating has less
mercury on the surface than in the middle of the layer
(Fig. 3) (coin number 15-15: 28 % Hg at the surface -between 45 % and 55 % in the center and coin number16-5 (41 % Hg at the surface - between 50 % and 60 % in the center). This difference is probably due to the preferential evaporation of mercury at the surface of the
coin. All the coins, with exception of the Strasbourg coin and number 21-36, have a core in copper with some
impurities in lead, tin, antimony and arsenic.