DOI Artikel:
Miazga, Beata; Paszkiewicz, Boris: The metal content of selected Polish and Brandenburg coins from the 14th and 15th centuries
DOI Seite / Zitierlink:https://doi.org/10.11588/diglit.49247#0158
BEATA MIAZGA, BORYS PASZKIEWICZ
154
in this specific group has been examined. The full-weight Brandenburg pennies from
this period show a fineness of about 780/1000, i.e. 12!4 lots.55 This tells us that the
“lighter” pennies were also made of a less valuable alloy.
The second coin (no. 20) is a full-weight penny, and since it is a perfect half,
we can reconstruct is original weight as being 0.56 g, which admittedly is still less
than the expected weight, 0.68 g, but the difference here can be attributed to the
small degree of precision at the mint or to the coin’s having been damaged. Here, the
silver fineness turned out not to be uniform, for it is higher in the interior (806/1000)
than on the surface (732/1000); however, as we can see, it still oscillates around the
level regarded as average.
A SUMMARY OF THE METALLOGRAPHIC ISSUES
The results that were attained in the course of our metallographic examinations
confirm that coins were sometimes enriched with silver on their surface.56 A number
of processes can cause this to happen. These include the technological processes
that are associated with the production of coins but also changes that result from
corrosion and conservation work.57 These processes are especially relevant when it
comes to raw materials made of various metals, but they also concern mint alloys.
The combination of silver and copper that is often used can serve as an example.
Coins struck from this material were often accompanied by an improvement in the
state of the coin’s surface. In comparison to the color of the original mint alloy,
a more silvery surface was attained, for example, via the process of “blanching”,
which consisted in pickling coins in order to remove the copper from the coin’s
surface. This happened through contact with acids, mostly organic acids.58 Another
process that could change a coin’s appearance had a similar character. When mint
alloys contain metals with different electrode potential values, that is, when one of
the metals is more precious than the other, one of them undergoes corrosion more
quickly than the other. As a result, this element - for example copper in combinations
of silver and copper - moves and becomes deposited on the “surface” of the coin,
which changes its elementary composition,59 as can be seen in some of the coins in
our collection. When oxidized-corroded coins are subjected to conservatory work,
yet another phenomenon can take place. The cleaning of a coin, whether this is
done mechanically or chemically, removes layers of impurities and corrosion, but
also part of the element, e.g. the oxidized copper. In effect, the clean surface of the
55 DANNENBERG 1997: 32.
56 BECK cl AL. 2004.
57 LINKE, SCHREINER 2000.
58 LA NIECE 1998: 119-120; LINKE, SCHREINER 2000.
59 LA NIECE 1998: 119-120; LINKE, SCHREINER 2000.
154
in this specific group has been examined. The full-weight Brandenburg pennies from
this period show a fineness of about 780/1000, i.e. 12!4 lots.55 This tells us that the
“lighter” pennies were also made of a less valuable alloy.
The second coin (no. 20) is a full-weight penny, and since it is a perfect half,
we can reconstruct is original weight as being 0.56 g, which admittedly is still less
than the expected weight, 0.68 g, but the difference here can be attributed to the
small degree of precision at the mint or to the coin’s having been damaged. Here, the
silver fineness turned out not to be uniform, for it is higher in the interior (806/1000)
than on the surface (732/1000); however, as we can see, it still oscillates around the
level regarded as average.
A SUMMARY OF THE METALLOGRAPHIC ISSUES
The results that were attained in the course of our metallographic examinations
confirm that coins were sometimes enriched with silver on their surface.56 A number
of processes can cause this to happen. These include the technological processes
that are associated with the production of coins but also changes that result from
corrosion and conservation work.57 These processes are especially relevant when it
comes to raw materials made of various metals, but they also concern mint alloys.
The combination of silver and copper that is often used can serve as an example.
Coins struck from this material were often accompanied by an improvement in the
state of the coin’s surface. In comparison to the color of the original mint alloy,
a more silvery surface was attained, for example, via the process of “blanching”,
which consisted in pickling coins in order to remove the copper from the coin’s
surface. This happened through contact with acids, mostly organic acids.58 Another
process that could change a coin’s appearance had a similar character. When mint
alloys contain metals with different electrode potential values, that is, when one of
the metals is more precious than the other, one of them undergoes corrosion more
quickly than the other. As a result, this element - for example copper in combinations
of silver and copper - moves and becomes deposited on the “surface” of the coin,
which changes its elementary composition,59 as can be seen in some of the coins in
our collection. When oxidized-corroded coins are subjected to conservatory work,
yet another phenomenon can take place. The cleaning of a coin, whether this is
done mechanically or chemically, removes layers of impurities and corrosion, but
also part of the element, e.g. the oxidized copper. In effect, the clean surface of the
55 DANNENBERG 1997: 32.
56 BECK cl AL. 2004.
57 LINKE, SCHREINER 2000.
58 LA NIECE 1998: 119-120; LINKE, SCHREINER 2000.
59 LA NIECE 1998: 119-120; LINKE, SCHREINER 2000.