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Quality grading turns visual impressions into repeatable descriptions. We study how colour, clarity, cut and carat weight are best observed and recorded, and how lighting, background and observer affect the result.
The aim is consistency: two examinations of the same stone, on different days, should arrive at the same description.
Hue, tone and saturation are judged in standardised daylight-equivalent lighting against a neutral background and master comparison stones.
Colour grading of diamonds and systematic colour description of coloured stones.
Reduces the influence of ambient light and individual perception.
Stones are examined at 10x magnification under darkfield illumination, and internal and surface features are plotted.
Assigning clarity grades and recording features that identify an individual stone.
Produces a permanent map that can be checked against the stone at any later date.
Optical scanners measure angles, percentages and symmetry, while polish is assessed under magnification.
Evaluating cut quality and comparing cutting styles.
Objective numerical data to accompany visual assessment.
No. Diamond grading scales were designed for diamond. Coloured stones are described using hue, tone and saturation together with clarity types suited to each species.
A stone can look noticeably different under warm, cool or mixed light. Standardised lighting makes descriptions comparable.
It can be assessed, but a setting hides parts of the stone and affects apparent colour, so results on mounted stones are given as ranges.
Establishing species and variety through optical, physical and spectroscopic measurement.
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Locating and modelling internal features in rough and polished stones.
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Relating proportions and symmetry to brightness, fire and scintillation.
Read MoreAdvancing the understanding of gemstones through science, precision and innovation, from their formation deep within the Earth to the finished stone.
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