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There are objective ways of identifying a good quality gemstone -regardless of asthetic appeal. Experts the world over look for the four C’s; carat, colour, cut and clarity, and then other qualities depending on the type of stone. For instance, rubies have what is called “rutile inclusions” which indicate that a gem has not been treated (good) but which may impair clarity (bad). Sometimes, these inclusions form a star pattern which is desirable amongst buyers (good).

The basics of quality are as follows:

Carat

Stone weights are measured in carats. Carats (ct) are divided into a hundred points (pt). It is important to remember that a stone that is twice as heavy will not be twice as big. Use the following table as a guide:

• 1pt 1.35mm
• 2pt 1.72mm
• 3pt 2.00mm
• 10pt 3.00mm
• 15pt 3.40mm
• 25pt 4.10mm
• 50pt 5.20mm
• 75pt 5.90mm
• 1ct (100pt) 6.50mm

Colour

The Colour grading scale of diamonds goes from D-Z. The best diamonds are in the D-F range and the most yellow are Z. Diamonds can even be muddy brown -these would normally be used for industrial purposes.

Cut

Diamonds have a high refractive index which means that they bounce light within themselves better than most substances -resulting in a brilliant display of sparkling colours. A well-cut diamond will reflect a lot of light back out of the “crown” of its cut (the top of the stone).

Clarity

Most gemstones have tiny imperfections called inclusions. These are different minerals that may show up as marks or other colours in the diamond. Inclusions near the crown will spoil the look of the diamond and its ability to reflect light. However, those near the girdle (where they are unlikely to be seen be the naked eye) are less of a problem. The scale is as follows:

• FL-1F

  • Internally flawless

• WS1 -WS2

  • Very, very slight inclusions

• VS1-VS2

  • Very slight inclusions

• SL2, SL2

  • Slight inclusions

• I1, I2, I3

  • Imperfect