How to detect faults in diamond
If one breathes on a diamond so that its dispersion is temporarily dimmed, a quick examination may help to detect spots or faults within the stone. As the cloud vanishes, black spots are more easily seen since they are not masked by refraction of light from the facets. The stone should be examined from different angles as the color may vary in different directions, or minute cracks may be more apparent in certain positions. A small crack may sometimes show a chromatic effect at certain angles only. A good lens is essential here and, of course, good eyesight.
It should be remembered that masses of stones appear deeper in color than single stones (more especially zircons and aquamarines). Light reflected from a mount may affect the color. For instance, yellow gold sometimes tends to impart its tinge on to a white stone, so all gems should be examined unmounted, if this is possible. With diamonds, the so-called fancy colored stones are scarce, yet they have no regular market value. They are often difficult to sell. Yet very few stones are really white. There is a fairly generally accepted name for each shade of color with diamonds, such as Jagers, rivers, Capes, all of which are used by experienced dealers in the trade, but these names do not, nevertheless, change the quality of a stone.