That is why most emeralds have a trade off between color and clarity. Accommodation of the color imbuing chromium atoms usually leaves the stones with complexion problems. Thankfully, these blemishes long ago ceased to pose a problem to the emerald trade. For centuries, dealers have been immersing the emeralds in various colorless cosmetic oils and resins. The line between natural oils and synthetic resins difficult to draw.
Many oils are in reality resins.
Like many products today they are often manufactured with stabilizing chemicals from other sources. Once an emerald has been treated it is extremely difficult to identify which category it belongs to because they are all closely related chemically. In many cases, due to re-treatment, one stone may contain a mixture of several substances. Before treatment After treatment Natural oils are not a permanent enhancement they dehydrate and leak out over time. Retreatment is usually enough to restore the stone to its old self.