The weight of a diamond is expressed in carats. One carat = 0,2 grams and one carat equals 100 points.
All diamonds have traces of their growth history. In gem-quality diamonds, this concerns minute internal and external characteristics, graded under Clarity. The clarity scale reflects the size, number and location of the characteristics when examined with a loupe 10 X.
The very best - and rarest - clarity is loupe clean. Most inclusions, however, are not visible to the naked eye unless magnified.
Colour - fluorescence
Most diamonds are colourless to slightly yellowish.
The colour grade is determined by comparison with a series of masterstones, the best grade being colourless. Diamonds can also occur in all sorts of colours, ranging from brownish to striking yellow, pink or purple, red, blue and green. These are called "fancy colours".
Certain diamonds can react to "black light" with grades varying from nil-slight-medium to strong.
Cut - proportions and finish grade
Fire, brilliancy and scintillation of a diamond are largely determined by the proportions of various part of the stone. Finish grade mainly evaluates the symmetry.
Diamonds can be cut in various shapes (e.g. square, pear or heart)
The round brilliant is probably the best known shape.