A plastic treatment that first appeared in Brazilian emeralds in the 1980's. The use of this treatment was not disclosed and was considered an unethical method of enhancement. The Opticon substance is green colored, but may turn yellowish over time. Many feel that Opticon treated emeralds are easily detected by their appearance when compared with typical untreated or cedarwood oil treated stones.

The original document is available at http://www.embassyemeralds.com/tiki-index.php?page=Opticon