Gemstone treatments explained

Emerald grows with natural surface-reaching fractures in almost every case, and it has been standard practice for centuries to fill those fractures with oil to improve transparency and reduce the visibility of inclusions. Traditional cedarwood oil is the most widely accepted form of this treatment and is considered a normal part of the emerald trade rather than a defect to hide.

Synthetic resins and hardened fillers are a more significant step up, because they are more permanent and can be harder to detect, and their presence should be disclosed as distinct from simple oiling. Any filled emerald, oiled or resin filled, is more fragile than an untreated stone and should never go through an ultrasonic cleaner, a steamer, or contact with solvents such as acetone, all of which can draw out the filler and leave the stone visibly more included.

Fracture filling in diamond uses a glass-like substance to fill a surface-reaching break and reduce its visibility, which is a treatment that can be unstable under heat, such as during a repair or resizing, and should always be disclosed. Laser drilling bores a microscopic channel to a dark inclusion so it can be bleached or lightened, leaving a tiny visible tunnel under magnification.

Both treatments are far less common in stones that have been in circulation since before the mid twentieth century, since the techniques are modern, and a diamond found in a genuinely antique setting is far more likely to be untreated. Any diamond suspected of fracture filling or laser drilling should be examined under magnification by a gemologist before a repair that involves heat.

Heat treatment of sapphire and ruby to improve color and clarity is standard practice across the trade and has been for decades. It is considered permanent, is accepted at every level of the market, and typically has only a modest effect on value compared with an unheated stone of comparable quality, which commands a premium mainly because unheated material is rarer.

Lattice diffusion is a different and more serious matter. It introduces color-causing elements only into the outer skin of a stone under very high heat, so the color does not extend through the body of the gem. A diffused stone can look convincingly saturated while carrying almost none of that color if it were ever repolished, and diffusion should always be disclosed as a distinct and more significant treatment than simple heating.

Natural turquoise is porous and often soft, and a large share of turquoise on the market, vintage and modern, has been stabilized with a colorless resin to harden the material and make it durable enough to set and wear. Stabilization is widely accepted and, disclosed, does not carry the same stigma as more deceptive treatments.

Dyeing turquoise to intensify or alter its color is a more serious treatment, since dye can fade or transfer with contact, and it should always be disclosed separately from stabilization. Irradiation is used on some other gem materials, such as certain diamonds and topaz, to alter color, and where it applies it should likewise be disclosed as a distinct treatment from heating.

Cultured and natural pearls are commonly bleached to even out their base color and are sometimes dyed to achieve colors that do not occur naturally, such as strong black or intense pink, both of which are long established and generally accepted treatments when disclosed. Coral has historically been dyed as well, particularly paler material dyed to resemble the more prized deep red tones, and dyed coral should always be identified as such.

Both bleaching and dyeing can be sensitive to strong light, heat and some cleaning chemicals over time, which is a further reason gentle, conservative cleaning is the right approach for organic gem materials regardless of treatment history.

A trained gemologist identifies most common treatments with a loupe or microscope, looking for characteristic evidence such as flash effects and trapped bubbles in filled fractures, a laser drill hole, an uneven color concentration consistent with diffusion, or dye pooling in a stone's surface-reaching cracks. Independent gem laboratories can confirm more difficult cases with spectroscopy and other instrumental testing.

Our practice is to note any treatment we identify or reasonably infer directly on the product listing, in plain language, rather than folding it into general marketing language. Where a stone's treatment history is genuinely uncertain, we say so rather than asserting either that it is treated or that it is not.

Every treatment described above changes how a stone should be cared for. Filled and oiled stones should avoid ultrasonic cleaners, steamers and solvents. Dyed and bleached materials should avoid prolonged strong light and harsh chemicals. Warm water, a soft brush and a soft cloth are safe for essentially all treated and untreated colored stones alike, and are what we recommend as a default.

On value, the general rule holds across gem types: the more permanent and widely accepted a treatment, the smaller its effect on price relative to an untreated stone of the same visual quality, and the less durable or more deceptive a treatment, the larger the discount should be. An honestly disclosed treated stone at a fair price is a reasonable purchase. An undisclosed one, discovered later, undermines trust in the entire transaction.