What is oiling in gemstone treatment?
By Jared James · Last updated 21 May 2026
Definition
Oiling is a gemstone treatment in which a colourless or lightly tinted oil or resin is introduced into surface-reaching fractures in a stone to make them less visible, improving the apparent clarity and depth of colour. It is most commonly applied to emeralds, which almost always contain natural fractures called jardin, and the treatment is so widespread in the emerald trade that it is considered a normal industry practice. The degree of oiling matters: minor filling is widely accepted, while heavy or coloured filler is considered more significant and must be disclosed.
Frequently asked questions
- Why are emeralds usually oiled?
- Emeralds almost universally contain inclusions and surface fractures, called jardin, that are part of the stone's natural character. Oiling fills these fractures to reduce their visibility and improve the apparent colour saturation, making a commercial-quality stone look considerably better without permanently altering the gemstone.
- Is oiling a permanent treatment?
- No, oiling is one of the few non-permanent gemstone treatments. The oil can dry out or be removed over time, especially if the stone is exposed to heat, ultrasonic cleaning or harsh chemicals. Oiled emeralds can be re-oiled by a jeweller if needed.
- What gemstones besides emeralds are oiled?
- Ruby and sapphire are sometimes oiled or treated with flux to fill fractures, and other coloured stones including alexandrite and tourmaline occasionally receive similar treatments. Any fracture-filling treatment should be disclosed when the stone is sold.
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