GRADING​

The rich colour of the finest tanzanite is quite unique in the gemstone world and in the case of tanzanite, colour is so important that it outweighs almost all other grading considerations.

In exceptional tanzanites, the colour is an intense violetish blue with red flashes of pleochroic colour coming from within the stone. Due to the gem’s strong pleochroism, fashioned examples typically show a mix of both blue and violet colours in a wide range of tones. As with most coloured gemstones, paler colours are more available and affordable than saturated ones.

Cutting plays an important role in tanzanite’s colour display. Because of its pleochroism—the ability to show different colours when viewed in different crystal directions—cutting direction determines the gem’s overall face-up colour.

Cutters consider financial realities when they decide how to cut tanzanite. As with other gems, weight lost is profit lost. Cutting a tanzanite to emphasize the violet-to-purple colour usually wastes less rough than cutting it to get a violetish blue colour. That is part of the reason face-up violet-purple tanzanites are more plentiful than specimens with a stronger blue colour component.

But this decision must be balanced against the higher per-carat price that the finer violetish blue colour might bring. The cutter essentially makes a choice between a smaller top-colour gem and a larger violet-purple one.