Judging Quality of Rubies and Sapphires                                  (RWH)

Next to red diamonds, rubies are probably the

most expensive of gems in the world in sizes

over 3 ct. 

The ideal for ruby is that of a red traffic

signal, a highly fluorescent red of high intensity.

Mogok Ruby, weight 15.97 carat

Unlike diamond, small amounts of silk in a stone

actually help the colour because they

scatter light into areas it would not otherwise go.

This helps cover up the extinc- tion which would

otherwise be found.

7.01 carat Mogok ruby

Thai/Cambodian rubies suffer the double

 deficiency of too much iron,which cuts the

 fluorescence, and no silk to scatter light.

Thai / Cambodian ruby

Top prices for blue sapphire are paid for stones of an intense blue verge- ing on the violet. 

Top color from the left 

Large sapphires are more common than large rubies. 

Colour zoning can be a problem in sapphire: look for stones which have no major zoning problems. Many blue sapphires are too dark in colour, especially those from basalt sources such as Thailand and Australia.

Such stones are generally inexpensive.

color zoned sapphire

Similarly, sapphires which are too light in colour

 

are also inexpensive.

The best stones are those which are well cut, eye

 clean and, most importantly, with intense blue

 colours.

Natural Sapphire with outstanding color and clarity 

Orange sapphires should be rich in colour without blackish areas. 

In star stones, transparency is an important factor.

Sri Lanka Star Sapphire 

Too much silk results in a lowering of colour

 

intensity, because the length of light paths

 

through the stone is reduced due to scattering

 

from the silk. 

The ideal star stone contains just enough silk to show a star, but not enough to cause the colour’s intensity to be reduced. A stone can be expensive if its colour is good, even if the star is poor. In contrast, stones with sharp stars but poor colour are not valuable.