Most emeralds have inclusions which can be regarded as its natural birthmarks that distinguish them as truly natural gemstones. Early gem merchants from India sought to enhance the color of emeralds by immersing them in clear oils and paraffin. They discovered that clear oils and waxes rendered surface fractures nearly invisible to the naked eye.
Today, most emeralds are oiled. Oiling is the oldest and most widely used treatment and is done in most places in the world. It is a process used to enhance the clarity of emeralds and is relatively easy to identify by a gemologists. In practice, clear oil is applied to the emerald and seeps into the emerald through surface fractures. Oiling is generally not permanent and may need to be
reapplied every few years. While colorless oil is considered an acceptable practice, the use of green oil is considered a deceptive practice.
Today, there are many sophisticated techniques with which to improve the clarity of emeralds. In addition, to oils and waxes, there are now clear resins called
Optic on that is sometimes applied to an emerald that seals surface fractures. In contrast to oiling,
Optic on is loner lasting. Optic on is considered an acceptable practice, except when green dye is used to enhance the emerald's color.