An Opticon emerald is an emerald that has been treated by impregnation with Opticon, a proprietary epoxy resin commercially developed for industrial sealing applications and adopted by the emerald trade as a clarity-enhancement filler. The treatment fills surface-reaching fissures within the emerald, reducing their visibility because the resin's refractive index (approximately 1.56) is close to that of emerald (1.577 to 1.583). Opticon filling is considered a moderate-to-significant clarity treatment, partially reversible under heat or solvents, and may yellow over time with exposure to ultraviolet light. Laboratories typically classify the treatment as 'minor' to 'moderate' clarity enhancement depending on the quantity of resin present, and disclosure is mandatory at every level of the trade.

The chemistry and the application

Opticon is a low-viscosity epoxy resin produced by the Hughes Associates company. It has a refractive index reported in the 1.55 to 1.56 range, depending on the specific formulation, which sits close enough to emerald's refractive index to produce significant reduction in fracture visibility when the resin is properly drawn into the stone's fissure network. The chemistry includes a hardener component that, when mixed in correct proportions and allowed to cure, produces a stable polymer network rather than a free-flowing liquid.

The application process involves cleaning the emerald thoroughly to remove any oil, dirt, or organic contaminants that would interfere with the resin's penetration, then placing the stone in a vacuum chamber with the prepared Opticon mixture. The vacuum draws air out of the fissures; releasing the vacuum pressure pushes the resin into the now-empty fissures by atmospheric pressure. The stone is then heated mildly to cure the resin in place, leaving the polymer network filling the fissure space.

Subsequent cleaning removes excess resin from the surface of the stone. The result is an emerald in which surface-reaching fissures appear less visible than before the treatment, with the resin reducing the optical contrast at the fissure boundaries.

Comparison with cedarwood oil

Opticon is one of several materials used to fill fissures in emerald. The traditional alternative is cedarwood oil, used for centuries in the emerald trade and still considered the most commercially acceptable treatment. Cedarwood oil has a similar refractive index to emerald, is non-toxic, biodegradable, and easily removed for re-treatment when needed. Its principal limitation is that it evaporates and migrates out of the fissures over time, requiring periodic re-oiling to maintain the apparent clarity.

Opticon is more durable than cedarwood oil because it cures into a polymer network rather than remaining a liquid. This makes the treatment longer-lasting in normal wear conditions, but also makes it harder to remove if the stone needs to be re-cut, repolished, or re-treated. Opticon is partially reversible under heat or aggressive solvents, but the reversal process is more demanding than simple oil removal and may damage the stone if not performed carefully.

The trade has historically considered cedarwood oil more acceptable than polymer fillers, on the grounds of reversibility and natural-substance precedent. Opticon is accepted in much of the trade but is generally considered a more significant treatment than oil and may affect resale value accordingly. Some markets — particularly in Asia and the Middle East — show stronger preference for oil-treated stones over polymer-filled ones.

Disclosure and laboratory reporting

Disclosure of Opticon filling is mandatory at every level of the trade. Major laboratories — GIA, AGL, GRS, SSEF, Gübelin, and the broader laboratory community — describe emerald clarity enhancement using standardised terminology that distinguishes oil filling from polymer filling and indicates the quantity of filler present. The standard descriptors are 'none', 'minor', 'moderate', and 'significant', applied to the cumulative volume of filler in the stone's fissures.

For Opticon specifically, laboratories typically identify the filler material by infrared spectroscopy, which reveals diagnostic absorption features that distinguish polymer fillers from natural oils and from each other. Some laboratories provide both the quantity description and the specific filler-type identification on the report; others provide only the quantity description.

For the trade, the laboratory documentation is the standard basis for disclosure to buyers. Sale of Opticon-filled emerald without disclosure exposes the seller to consumer-protection action and to industry sanction; accurate disclosure protects both the buyer and the seller and supports the long-term integrity of the emerald trade.

Stability and aging

Opticon treatment is considered partially stable in normal jewellery use. The cured polymer is durable enough to survive routine wear, cleaning with mild soap and warm water, and ordinary handling. However, several conditions can degrade or remove the treatment: sustained exposure to ultraviolet light may cause yellowing of the resin (changing the apparent body colour of the stone); ultrasonic and steam cleaning may dislodge or fracture the cured resin; aggressive solvents (acetone, strong alcohols) may dissolve or weaken the resin; and prolonged heat (such as occurs during repair work near the stone) may soften or dissolve the resin.

The practical implication is that Opticon-filled emeralds require more careful long-term maintenance than naturally clean emeralds. Re-treatment may be required every several years to maintain the original apparent clarity, particularly if the stone has been exposed to UV light or to repeated cleaning. The maintenance cost is modest but real, and buyers should be informed of the requirement.

In the trade

For working dealers and jewellers, Opticon-filled emeralds are a defined and legitimate commercial category, occupying a price point above untreated stones of equivalent visual clarity but substantially below the same untreated stones if such existed in any quantity (which they generally do not — virtually all commercial emeralds have some level of fissure filling). Buyers seeking commercial-grade emerald should expect some filling and should select stones whose laboratory documentation indicates 'minor' filling rather than 'significant' filling.

See also Opticon filling, cedarwood oil, emerald enhancement, and emerald for related entries.

Further reading

• GIA Gems & Gemology — emerald enhancement and laboratory practice
• AGTA — coloured stone treatment terminology
• International Gem Society — emerald treatment reference