Page:A treatise on diamonds and precious stones including their history Natural and commercial.djvu/44

 of any stone when close set, and not to decide until it is taken out, as the most practised eye may possibly be deceived by the various artifices of placing foil, patching that foil coloring, &c. The most simple and best method of determining whether a substance is diamond or paste, is to apply a very fine file to the girdle, which produces no effect upon the diamond, while paste or composition are easily abraded by it; and if the girdle or projecting angle of a diamond be applied to stones which deface the file, as white topaz, sapphire, &c. it will instantly cut them, the diamond having no rival that approximates to it in hardness. But it is by no means advisable to apply this test with a valuable diamond, as it might possibly produce a flaw.