Opticon

Nearly all emeralds are treated with a liquid or resin after cutting. The most popular filler is a synthetic polyester epoxy resin called Opticon. Opticon is nearly transparent and light amber in color. The refractive index is approximately 1.545. Treaters may use green Opticon to improve the color of emeralds without proper disclosure. Opticon may turn yellow after many months/years. With some training, proper magnification and comparison stones you should be able to detect dispersion flashes, trapped gas bubbles, and unique texture (s) inside the stone. All treatments should be disclosed at all levels of the distribution chain. If you are doubtful have it checked by a reputed gem testing laboratory.