Jan 99:  The First Emerald Congress held  in Bogota, Columbia concluded the only adequate treatment for emeralds was cedar oil.

Today, most emeralds are typically treated with a variety of substances in an attempt to hide or mask fissures within the gemstone.

Antonio Negueruela markets a purified cedar oil in which the color is suppressed. The oil has a high density and a refractive index similar to that of emerald.

One source uses a process similar to this:

"The emerald is to be placed in a container and covered with alcohol. The alcohol is to be heated slowly up to a maximum temperature of 50 C in order to remove any foreign substances. Once the emeralds have been cleaned, they are to be placed in a glass container and covered with the purified cedar oil to a minimum of 3 centimeters above the top of the stones. The container is then heated slowly up to a maximum of 90 C and then left to settle to room temperature over a period of 12 hours. Once the liquid is cold, the emeralds are to be removed and placed on a clear absorbent paper. Then they are to be dried with a cloth and then rubbed with a duster."