By the following simple method, the legend or inscription upon a coin
may be read in absolute darkness. Polish the surface of any silver coin
as highly as possible; touch the raised parts with aqua-fortis, so as
to make them rough, taking care that the parts not raised retain their
polish. Place the coin thus prepared upon red-hot iron, remove it into
a dark room, and the figure and inscription will become more luminous
than the rest, and may be distinctly seen and read by the spectator. If
the lower parts of the coin be roughened with the acid, and the raised
parts be polished, the effect will be reversed, and the figure and
inscription will appear dark, or black upon a light or white ground.
This experiment will be more surprising if made with an old coin, from
which the figure and inscription have been obliterated; for, when the
coin is placed upon the red-hot iron, the figure and inscription may be
distinctly read upon a surface which had hitherto appeared blank.
This experiment may be made with small coins upon a heated poker, a
flat iron, or a salamander. The effect will be more perfect if the
red-hot iron be concealed from the eye of the spectator: this may be
done by placing upon the iron a piece of blackened tin, with a hole cut
out, the size of the coin to be heated.