For
tests of stones harder than quartz, take stones of known hardness, as
diamond, ruby, sapphire, and topaz, find a smooth polished place on the
edges of both stones used, and draw them across each other; that which
scratches the other is, of course, the hardest. If the stone being
tested is the softer one, try it with other known stones of less
hardness than the first used, until its place in the scale is found. If
it is harder, reverse the process.
Observation
of the facet edges of a stone under the loop will give an idea of its
hardness, as the edges of a soft stone are more or less rounded; they
cannot be cut to the sharp edge of the harder gems.
In making a test of hardness, judgment must be used to avoid damage to valuable stones.
