If the cut is too deep light also escapes through the opposite direction. When a diamond is cut to good proportions, light is reflected from one facet to another and then dispersed through the top of the stone. Most natural colored gemstones are treated or enhanced to intensify color, diminish imperfections or improve durability. The following are examples of the most commonly used and accepted treatments for different types of colored gemstones. The oiling of emeralds is an ancient process used to enhance the clarity of the emerald.
Oil is applied to the emerald which seeps into the fissures, which reach the stone's surface.
Along with improving the clarity, this process may prevent brittleness. Oiling is not permanent and may need to be reapplied every few years. Take care not to hit the stone on hard surfaces as this may chip or crack the emerald due to the natural brittleness of the stone. Special care should be taken when cleaning emeralds. Since heating is generally permanent, heated stones do not normally require special care.