Off-Colour — Trade Term for Hue Outside the Desirable Range
Off-Colour — Trade Term for Hue Outside the Desirable Range
A category designation for stones whose hue, tone, or saturation reduces market value, distinct from off-cut quality issues
Off-colour is a trade term describing a gemstone whose hue, tone, or saturation falls outside the desirable range for its species, resulting in reduced market value. The designation is subjective and market-driven; what is considered off-colour varies by species, regional preference, and the specific buyer's standards. Off-colour stones may exhibit undesirable secondary hues (brownish or greyish modifiers, for example), insufficient saturation, or tones that are too light or too dark for the intended market. Off-colour material trades at significant discounts to the principal commercial range and may be candidates for re-cutting, treatment, or sale into secondary markets.
What makes a stone off-colour
The off-colour designation can apply for several distinct reasons. Wrong hue describes stones whose dominant hue falls outside the species' commercial range — a yellowish-green emerald, for example, or a brownish ruby. Wrong tone describes stones too light or too dark for the principal market — a sapphire so dark it shows extinction across most of the table, or one so light it appears washed out. Wrong saturation describes stones with greyish, brownish, or otherwise muted colours that lack the cleanness and vibrancy that command premium prices.
The criteria are species-specific. A medium-tone slightly bluish ruby is acceptable; the same hue on a sapphire would be off-colour for that species. The same medium-strong green colour is excellent for emerald, ordinary for tourmaline, and below par for tsavorite. Buyers and sellers use the off-colour designation as shorthand for the broader concept of not in the principal commercial range for the species at hand.
Distinction from off-cut
Off-colour is distinct from off-cut, which refers to cutting-quality issues such as poor proportions, asymmetric facets, windowing, or extinction caused by faceting rather than colour. A stone can be off-colour but well-cut, off-cut but well-coloured, or both off-colour and off-cut. The terms are used together and separately depending on the issue.
Re-cutting can sometimes improve the apparent colour of a stone, even if the underlying body colour is off-colour for the species. A deeper pavilion can darken a too-light stone; a shallower pavilion or a window cut can lighten an over-dark stone. These corrections are limited and cannot transform genuinely poor body colour into desirable colour, but they can shift a marginal stone toward acceptability.
Treatment as a response
Off-colour stones are common candidates for treatment. Heat treatment can shift hue and improve saturation in many sapphires, rubies, and tanzanites. Irradiation can improve colour in some topaz and quartz varieties. Diffusion can alter the surface colour of corundum. Treatment status must be disclosed in commerce, but the effect of treatment on value is positive when the treatment improves the stone's appearance from an off-colour starting point.
The economics of treatment are central to the trade in lower-grade rough. Off-colour rough is purchased at low prices, treated, and sold at significantly higher prices reflecting the improved appearance. The treatment cost is generally low relative to the value uplift; the principal economic risk is that treatment fails to achieve the expected colour shift, leaving the seller with treated material still off-colour and now disclosed as treated.