Question 1

How can I tell a natural star sapphire from a synthetic?

Accepted Answer

Synthetic star sapphires often show a very sharp, uniform star that looks painted on, very even colour, and curved growth lines or gas bubbles under magnification. Natural stones usually have slightly irregular rays and natural inclusions. These are only indicators, and diffusion-induced stars add a further complication, so a laboratory report is the reliable way to confirm a natural stone.

Question 2

Are star sapphires treated?

Accepted Answer

Many are not, since heating at high temperatures dissolves the rutile silk that creates the star. However, some stones are heated at lower temperatures, and surface diffusion of titanium has been used to create artificial stars. Any treatment should be disclosed and it changes value considerably. A lab report states which treatments, if any, have been detected.

Question 3

What is a twelve-rayed star sapphire?

Accepted Answer

A twelve-rayed star appears when two different sets of oriented needle inclusions are present, producing two overlapping six-rayed stars. It is seen most often in black star sapphires, although it occurs in other colours. These stones are collected for their rarity, and as with any star sapphire, the sharpness and completeness of the rays drive value.

Question 4

What colour of star sapphire is most valuable?

Accepted Answer

Fine blue star sapphires with a sharp, centred star and saturated body colour are generally the most valued, followed by other attractive colours such as pink and purple. Grey and black star sapphires are more affordable. Within any colour, the combination of star quality, body colour, translucency and size determines price rather than colour alone.

Star Sapphires