Diamond Grading Reports

A Diamond Report or 'Certificate' is a written description of the identity and quality of a genuine diamond, issued by an independent authority.

A diamond report will confirm the stone is a genuine diamond and will describe its quality, enabling you to buy with confidence. Any treatment used to enhance the beauty of the diamonds will be identified. The report will enable your jeweller or valuer to establish the current market value of your diamond when you need to insure your jewellery.

Diamonds can be graded accurately only if they are loose. If mounted in jewellery only an approximate judgment of the diamond’s quality is possible. To calculate the weight of a mounted stone, the use of measuring gauges and mathematical formulae can be employed to convert diamond dimensions to carat weight but inevitably, errors will creep into such calculations. Hence the desirability of unsetting fine diamonds to weigh them accurately on an electric carat balance. Such balances usually weigh to three decimal places, e.g. 1.345 carats. This weight can be noted but in diamond commerce and on diamond reports, carat weights are expressed to the second decimal place, i.e. 1.34 carats. According to CIBJO, the international jewellery confederation, the third decimal place can be only rounded up if it is a nine, so 1.349 carats can be expressed as 1.35 carats whereas 1.348 carats is reported as 1.34 carats.

A diamond is colour graded with its table facet down on a flat surface and is viewed at a direction parallel to its girdle plane, within a purpose built viewing box fitted with special corrected lamps which provide a neutral daylight illumination with a negligible amount of ultra-violet light. It is this UV light present in normal daylight and some display lighting which causes a number of diamond to glow blue. This fluorescent effect can affect the way our eyes perceive the colour grade of the stone. Usually diamonds which fluoresce strongly (‘medium’ to ‘very strong’ intensities) will appear a ‘better’, i.e. less yellow, when exposed to UV rich light because the blue glow masks the true yellow colour of the stone. Some diamond dealers do not like fluorescent diamonds and will trade them at a discount to non-fluorescent stones.