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No oil emeralds are the rarest form of emerald on the market today. The oiling of emeralds is one of the oldest practices in the gem trade, clear oils or resins are worked into the stone’s natural fissures and cracks, enhancing their appearance and depth of colour. The practice is so widely used that gemmologists grade the degree of enhancement on a scale.
Genuinely untreated examples are exceptionally rare. They only exist where the rough possesses such clarity that intervention is not required, something almost exclusively encountered in material from the old mines of Muzo and Chivor, which supplied Europe’s jewellers from the sixteenth century onwards. No oil emeralds now survive almost entirely in antique and vintage pieces; their supply was finite and is no longer replenished.
Each no oil emerald ring in our collection is accompanied by independent lab certification confirming its untreated status.
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To understand what “no oil” means, we must first understand the treatment process and why it may not be suitable for all emeralds. Emeralds are naturally a very included stone and thus are routinely oiled to improve their clarity and colouration. The oil (or resin) is interspersed into the emerald through the use of a vacuum or gentle heating. This removes the air from the fissures within the emerald and forces the oil into surface-reaching cracks. Any excess oil is then wiped away from the stone, leaving it with a clearer, more refined appearance.
“No oil” refers to the condition of the emerald at the time of testing. While most emeralds are graded on a scale from minor to significant, depending on their level of enhancement, an emerald with the classification “no oil” on its gemmological report indicates that no oiling can be observed within the stone. As a result, these stones are highly prized by collectors for their exceptional natural clarity and colour.
When emerald deposits were first discovered in the old mines of Colombia (Muzo and Chivor), the quality of material was far superior to what the mines are producing today. This meant crystals of vibrant colour and higher clarity. This standard of material required fewer treatments to achieve stones of exceptional quality.
It was these stones that began supplying European courts throughout the 16th century, handcrafted into exceptional jewellery pieces and appreciated across the world. As time went on and deposits of finer material became more scarce, treatments were increasingly applied to enhance the overall appearance of the gemstones being discovered.
This means that genuinely untreated “no oil” emeralds are today mainly found in antique pieces, preserved in their natural state.
A true “no oil” emerald should always be verified by a respected gemmological laboratory. However, there are a few visual clues which can help identify a “no oil” emerald. Under magnification, you can look for untreated fissures and cracks within the stone; these should appear sharp and well-defined, indicating no oil has entered the gaps.
Further to this, tilt the gemstone under light and look for flashes of yellow, orange, or blue. These flashes can indicate oil-filled fractures, caused by light interacting with the treatment agent.
Although these tests can be a good indicator of treatments, gemmological certification is the only definitive way to confirm a “no oil” emerald. To ensure this is accurate, it is recommended that certification is carried out independently by coloured stone laboratories such as SSEF and Gübelin.
No oil emeralds are part of the beryl family, scoring between 7.5 and 8 on the Mohs hardness scale, making them suitable for everyday wear. However, it is recommended that you remove your ring during activities where it may be likely to get damaged, such as at the gym or while gardening. While the crystal is naturally quite strong, untreated emeralds have many cracks and fissures which can cause them to chip more easily, so care should be taken.
As no oil emeralds are slightly more vulnerable gemstones, we recommend that you do not soak or brush them, as this could cause damage. Instead, simply give them a wipe with a soft cloth to remove any dirt or oils.
No oil emeralds are the most sought after by collectors and connoisseurs alike for their scarcity. As emerald mines no longer produce the quality of material they once did, treatments must be used to ensure a marketable product. This means that most no oil emeralds have already been mined and were a finite resource, adding to their increasing value and desirability.
Oil status is verified by gemmological laboratories through detailed microscopic examination and rigorous testing. The surface is closely inspected for fissures under high magnification, searching for signs such as the “flash effect” or any remaining oil or resin within the cracks. Fibre optic lighting and spectroscopy may also be used to identify any oils or resins present within the fissures. If there is no evidence of enhancement at the time of testing, “no oil” will be stated on the report.