Emerald Oiling: The Traditional Clarity Treatment Explained

Emerald oiling: the traditional clarity treatment explained

What emerald oiling is

Oiling is the practice of working a colourless oil into the surface-reaching fissures that occur naturally in most emeralds. Emerald belongs to the beryl family and forms under conditions that almost always leave the crystal with internal inclusions and fine fractures, many of which reach the surface. Filling those fissures with a substance of similar refractive index makes them far less visible, improving the stone's apparent clarity and overall appearance. Oiling does not change an emerald's grade or its underlying clarity; it improves how the stone looks.

Why emeralds are oiled

Because surface-reaching fissures are so common in emerald, oiling has been accepted in the gem trade for a very long time. It is regarded as the standard, routine treatment for emeralds — so widely practised that the great majority of emeralds on the market have been clarity-enhanced to some degree. Disclosure of the treatment is expected, and reputable laboratories such as GIA report the presence of clarity enhancement and, where it can be assessed, its degree, typically described as minor, moderate or significant.

Cedar wood oil, the traditional natural choice

The classic material for oiling emeralds is natural cedar wood oil. It is a colourless natural oil whose refractive index is close to that of emerald, which is precisely why it works so well: light passing through a filled fissure is bent in much the same way as it would be through the surrounding gem, so the fracture becomes less visible. Because it is a natural oil rather than an artificial resin, cedar wood oil is considered the traditional and most conservative way to treat an emerald.

A treatment that is refreshed over time

Oiling is non-permanent. Over the years, exposure to heat, solvents, ultrasonic cleaning, or simply the passage of time can cause the oil to dry out or escape from the fissures, and a stone that once looked clear may begin to show its fractures again. This is normal and expected. Because the treatment can deplete, an emerald can be re-oiled, and periodic re-oiling is a normal part of caring for the stone over its lifetime.

Re-oiling versus full retreatment

There are two broad approaches to refreshing an oiled emerald. The first, often called a re-oil or refresher, simply introduces fresh oil into the existing fissures without disturbing whatever filler is already present; this is the lighter and more common need. The second, a full retreatment, involves first removing the existing filler and then treating the stone again from a clean starting point. A full retreatment is generally reserved for stones that have been over-treated or poorly treated in the past, where the old filler is best stripped out before fresh oil is applied. For most emeralds, a simple re-oil is sufficient.

Caring for an oiled emerald

Because oiling can be depleted by heat and harsh cleaning, emeralds should be handled gently. Avoid ultrasonic and steam cleaners, and avoid solvents and high heat. Warm water and a soft cloth are the safest way to clean an emerald at home. Handled with reasonable care, an oiled emerald will keep its appearance for many years, and can be re-oiled if and when its fissures begin to show again.

Skyjems offers an in-house emerald oiling and re-oiling service using natural cedar wood oil; details and pricing are on our service page.