Example 2: "Reliquary"
The surface of the artifact was first divided into two
layers: a tarnishing layer and an alloy layer. But all at-
tempts to make the fit ended well, until we introduced a
third layer: a layer of pure silver. The fit has become
better, although not perfect, the approximation error has
decreased. This can be seen on the plot (Figure 4).
Figure 4. Experimental XRF spectrum and two types of fit, where there are two and three layers, respectively
We have one explanation why the silvering was
done with absolutely pure silver without any impurities
in the 17th century. Even before Boulsover's invitation
in 1742 (Sheffield plate), there were two methods [17]
of industrial silvering: French coating [18] (or French
Plaque) and close coating. The first method was in-
vented in the early 1700s and used for electroplating
later. Brass or copper, polished and degreased and heated
almost to red hot before being placed in nitric acid. Silver
plating was the application of four to six silver sheets.
The sheet was also heated and then quickly and under
pressure was applied to the surface. The sheets silvered
by this method were specially marked indicating the
thickness of the silver. The thickness was 6 to 33 μm min-
imum.
Example 3: "Modern jewelry"
The third example is related to the Raman spectrom-
eter (Figure 5). We use the method of comparing spec-
tra based on correlation coefficients (one of at least
four methods). The correlation coefficient r is in the range
-1 .. +1 where the correlation r = 0.95 corresponds to an
error δ = 15%, according to pharmacologists [19].
Since a possible maximum δ = 30%, the correlation
coefficient r can be 90%.
Figure 5. Raman spectra of Ag2S: a) experimental (more smooth) and b) Martina (less smooth) [20]
It is not enough to fit the spectrum with a given error,
because people know tens of millions of organic and hun-
dreds of thousands of inorganic substances, even if mix-
tures are not yet taken into account (Although it is the
mixtures that are more common). No database includes
that many. It is necessary to limit the number of possible
formulas in any way. We used a portable XRF device.
XRF completely eliminated any organic compound simply
due to the sum of the number of pulses, еxcluded at least
in a noticeable amount. The peak of Light Elements, gen-
erating organic matter (H; C; O; N) and air (mainly), is
less than 1 keV and is poorly recorded by the built-in
receiver. Also, C - O - F is more transparent to X-rays,
and the resulting photon goes not only to the receiver,
but in all directions. The distance increases as x, and the
receiver area decreases as x
2
. XRF allows determining
the position of silver, for example, light elements (or-
ganic matter) are located before or after the silver foil.
№ 10 (91)
октябрь, 2021 г.
71
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