Two stones can look identical to a casual eye and differ tenfold in price. The difference comes down to four value factors professionals weigh: colour, clarity, carat and cut.
Colour
In coloured stones, colour is the most important factor — hue, tone and saturation together. A stone with vivid, well-balanced saturation commands a premium over a pale or overly dark one of the same variety. In diamonds, the scale runs from colourless towards tinted, and the top grades carry steep premiums.
Clarity
Clarity is the presence of inclusions and surface features. Each gem variety has its own clarity expectations — some types almost always form with inclusions, so the standard differs by stone. What matters is how inclusions affect beauty and durability, not their mere existence.
Carat and cut
Carat is weight, and price rises non-linearly: a 2-carat stone of equal quality costs far more than two 1-carat stones, because large clean rough is rarer. Cut covers both shape and quality of fashioning — proportions that return light to the eye in faceted stones, and skilled shaping in cabochons. A poor cut drains value from fine rough.
Learning to judge
Practical colour description, clarity types, cutting styles and carat interpretation are taught hands-on with real stones in the gem curriculum at JDMIS — see the gem and jewellery trade programme for the full pathway.