Assessing Color and Quality in Blue Gemstones
Gemologists assess color by considering hue, tone, and saturation. Gemstones often have a secondary hue in addition to a primary hue. For blue gemstones, common secondary hues are green and violet. In general, a more pure blue hue is desirable, and when a stone strays further from blue, it’s less valuable. Still, greenish blue and violetish blue gems are quite attractive! Blue sapphires with slight violet hues are still top color. Other gems, such as paraíba tourmaline, more commonly exhibit green secondary hues.
Blue hues reach top saturation, or intensity, at medium-dark tones, about 85%. This is called the gamut limit. Vivid saturation is an eye-popping color. Darker tones will appear inky or steely, while lighter tones may appear washed out or gray. Nevertheless, beautiful blue gemstones occur in a wide range of tones, from light, sky blues to deep, dark colors.
Clarity grades have much less importance in blue gemstones than in colorless stones. Since the color can mask inclusions, it makes them less noticeable. However, avoid large inclusions or fractures, as these can still make the stone more breakable. For lighter toned blue gemstones, a somewhat…