Loose Gemstones for Sale

How to judge a loose colored stone

Color decides most of the value in any colored gem, and it has three parts.

• Hue is the color itself. A pure hue is worth more than one with brown or gray in it.
• Tone is how pale or dark it is. The best stones sit deep but still let light through.
• Saturation is intensity. More intense color increases value in every gem.

After color come clarity, cut and size. How much clarity matters depends on the gem: some are expected to be clean, and emerald is expected to have inclusions.

Two cutting faults to check before you buy

Colored stones are often cut to keep weight rather than to return light. Two faults follow.

• Windowing is a pale, see-through patch in the center of a stone cut too shallow.
• Extinction is dark, dead areas that appear as the stone tilts, from a cut that is too deep or a tone that is too dark.

Both are easiest to judge in ordinary indoor light rather than under bright spotlights.

Treatment, disclosure and the certificate

Treatment is normal in colored stones, and the right question is what was done and whether it is disclosed.

• Heating is permanent and widely accepted in many gems. Unheated stones are rarer and carry a premium, and they are our buying focus.
• Oiling is standard in emerald, graded from none to significant.
• The certificate from GIA, SSEF, Gübelin, GRS or AGL confirms natural origin, treatment and, for stones where it matters, geographic origin.

Planning the setting

• Hardness decides where a stone can go. Ruby and sapphire at 9 suit any ring. softer stones are safer in earrings and pendants.
• Carat weight does not mean size. Gems differ in density, so a one carat stone of one gem can face up larger or smaller than another.
• Shape affects spread. Ovals, pears and marquises face up larger per carat than rounds and cushions.