People familiar with emerald jewelry may already also be familiar with the common treatment processes that emeralds often go through. In the gemstone trade, many different species and vareties of gemstones undergo treatment procedures to improve aspects of their beauty and / or duarbility. For rubies and sapphires it's usually exposure to heat treatment. For emeralds on the other hand, a treatment called fracture-filling is the most commonly done procedure.
What is fracture filling? Well, some gemstones tend to be found with more inclusions or fractures compared to other kinds. Emerald is one of these gemstones, and it is usually very highly included with cracks, minerals, internal debris and all sorts of things. Many traders, in the efforts to improve emerald's transparency, subject the stone to some sort of filling- usually the material used is either oil, natural resins, artificial resins or proprietary polymers. Oil is the oldest and one of the most common substances used, therefore many in the jewelry business readily recognise the term- oiled emerald.
If your emerald is oiled, and you're not quite familiar with what this means, don't fret. Oiling is a very common practice for emerald, as a type of fracture-filling procedure. Over 90% of gem-quality emeralds are estimated to undergo some form of filling procedure in today's markets. A premium price point does exist for emeralds that are untreated though.
Oils and other filling substances have a refractive index closer to that of the surrounding emerald's, and this makes fractures less visible to the eye, nearly concealing them at times, and making a stone look more clear and beautiful than it originally was. In the above-image you can see the before-and-after shots of an emerald that underwent a fracture-filling treatment (although a proprietary filler was used for this stone, oiled emeralds would essentially look similar in terms of the general effect that improves apparent clarity).
Oils can gradually seep or 'sweat' out of emeralds over long periods of time (years usually). Heat or excessive light exposure can also hasten the oil leaving an emerald's fractures. The process can be re-done again though, by an experienced gem treater. Some substances, especially proprietary fillers made by branded companies, have a warranty that fillers can be removed without any damage to the stone, and then re-done easily. Not all though allow for this, and occasionally you will see some emeralds with residue of stuck-fillers nestled between cracks and fissures in the stone.
Depending on the degree of fracture-filling, many emeralds may require special care in cleaning. Ultrasonic or steam cleaners may not be advisable for heavily fractured emeralds or for stones that were treated in significant areas.
