How does oil treatment affect emerald value?

Minor cedarwood oil treatment is basically a standard practice, and it helps maintain an emerald’s market value, but if someone does moderate or heavy oiling or uses artificially coloured resins, then the price goes down quite a bit.

Since nearly all emerald stones have fractures that reach the surface, oiling has been used for a long time to improve the stones’ overall clarity, and this matters in real ways. Gemmological laboratories even state the degree of this treatment, from “none” up to “significant” on a clear scale. An emerald that is verified as having “no clarity enhancement” is exceptionally rare, and it can cost a small fortune compared with typical oiled stones.