ThinLayerAnalysis
Thickness of Silver Plate on Silver Plated Goblet
This silver
plated goblet was purchased from an antique shop. It looked
like it had
received a lot of polishing during its life and the base metal,
brass, was showing through around the rim and the lower part
of the bowl. This fact certainly influenced the
price. It
is not pretending to be anything other than what it is, as it has
'silver
plated' stamped on the base.
The
plating around the outside of the goblet is obviously very
worn (with a thickness of less than zero in places) and it
would be interesting
to know how thick it was when it was made.
Assuming
that the plating thickness was uniform over the goblet, the
least worn area appeared to be the underside of the base, and a ball
crater measurement was made here using a 30mm ball. Using
this hidden area
also meant that no further damage was done where it would be seen.
During the cratering set up it was noticed that the silver was
very soft. Under the
microscope, a simple wipe with a finger left significant scratches.
The above picture shows a crater of about 0.75 mm diameter, leading to
a silver thickness of just 2.2 µm. In
comparison, the plating thickness
of quality silver plated cutlery is typically at least 35 µm.
Presumably the goblet was designed to be decorative
or for very light use.
This investigation displays a major advantage of the ball crater method
as the less than 1 mm diameter spot is the only damage made by the
conclusive measurement. If necessary this area could be
replated
locally, leaving only a very shallow depression (a few µm).
This investigation also demonstrates that such measurements
can
be made on curved surfaces.
