Journal

Emerald clarity enhancement: oil, resin and what a report says

Guide · · Maedot

Most emeralds sold today have had their fissures filled with a colourless oil or resin so that the cracks show less. In 1999, GIA researchers wrote that laboratories estimated about 90% of the emeralds they saw had been clarity-enhanced. A laboratory report tells you whether a stone shows filling, how much, and, if you ask, what kind of filler. It describes the stone only on the day it was tested.

Why emeralds are filled

Emerald usually grows with fissures, and mining and cutting add more. Air in a fissure that reaches the surface scatters light and shows the crack. A filler with a refractive index close to emerald's hides it and, because less light scatters, also improves the apparent colour.

Oil and resin

Cedarwood oil and Canada balsam are the traditional fillers; epoxy resins such as Opticon came later. A 1991 GIA study found Opticon somewhat more durable than the two traditional fillers, but cleaning and jewellery work affected all three. Oil can be removed and renewed. Hardened resin lasts longer but can degrade, and is then hard to remove. A paper from Colombia's CDTEC laboratory, presented in October 2025, says cedar oil is now used less than mineral oil and liquid or hardened artificial resins. The type matters to buyers: in 1999 GIA noted that some markets take emeralds less readily if they are thought to contain resin rather than cedarwood oil.

How laboratories grade it

Since early 2000, GIA has graded clarity enhancement as minor, moderate or significant (F1, F2, F3), from the size, number and position of filled fissures. Minor means a slight effect on the face-up appearance; significant means an obvious one. This rates the treatment, not the stone's clarity, and GIA's original study stressed that a significant grade does not automatically mean low value.

The Laboratory Manual Harmonisation Committee (LMHC), whose seven members include GIA, Gübelin and SSEF, sets shared wording in its Information Sheet 5, last revised in May 2025:

  • No indications of clarity modification, or no fissures at all.
  • F1, F2 or F3. A minor, moderate or significant amount of filler in fissures. Naming the filler is optional.
  • C1, C2 or C3. Resin or wax in wider fractures and cavities, graded separately.
  • Emerald and resin. A stone held together by resin, described as a manufactured product.

Gübelin dropped its "insignificant" category on 1 November 2025; those stones are now reported as showing no indications of clarity enhancement. SSEF states the filler and its amount on its reports. AGL, which is not an LMHC member, still uses words such as insignificant, minor and moderate, and names the filler. Since 15 December 2024, GIA can identify the filler on request, as Type A (oil, wax or natural resin), Type B (artificial resin) or not identifiable; its US fee schedule from 1 July 2026 charges $50 for this on top of the report.

A report is a snapshot

Filling can usually be reversed and repeated, so LMHC wording limits a report to the stone's condition at examination. In June 2026, SSEF warned that emeralds it had tested were being refilled and sold with their old reports, which showed little or no filling. It advises having a fissured emerald with an older report retested, especially one that looks unusually clean.

Care and disclosure

GIA advises against ultrasonic and steam cleaners for emerald: vibration can weaken a fractured stone, and steam can drive out oil or unhardened resin. Warm soapy water and gentle scrubbing are safest. The LMHC recommends taking a filled emerald out of its setting before jewellery repair.

In the United States, the FTC's Jewelry Guides say sellers at every level should disclose a treatment that is not permanent, that needs special care, or that significantly affects value. Emerald filling meets the first two tests.

Buying emerald from Maedot

Each selection lists the stated origin and any treatment or testing on record. Ask about any fissure you see; you can look at the stones in Addis Ababa, by live video or through samples.

Sources

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