Cutting rough emeralds is one of the most difficult and stressful tasks any gem-cutter will face. Emeralds fall between a 7.5 and 8.0 on the Mohs scale of mineral hardness, and they are quite brittle, making them susceptible to cracking and splintering. They are also incredibly valuable, with high-quality emeralds surpassing even diamonds in cost-per-carat, making even the smallest mistake quite costly. Because of the difficulty inherent in cutting emeralds, most high-quality stones are cut by experts who specialize in emeralds alone -- many gem-cutters do not touch emeralds unless it is a special situation. However, for those with the patience and the luxury of being able to mess up occasionally, cutting rough emerald can be an incredibly satisfying and lucrative undertaking.
How to Cut Rough Emeralds
Choose a cut for your emerald. The most common cut is named after the stone itself: an emerald cut. This is the classic rectangular shape with beveled corners, which allows light to capture the deep green of the stone and reduces stress on the stone to prevent cracking. Medium-quality or highly-included emeralds are generally cut into polished, round cabochons. Lower-quality emeralds are often made into round beads.
Cut the rough emerald down to the general shape you've decided on. Use a circular saw for flat lines, and a jigsaw for curved lines. Make sure to use a blade with a hardness sufficient to cut the emerald -- preferably a diamond blade.
Facet the stone using a faceting machine. Attach the rough emerald to the faceting peg, either with clamps or with hot glue. Direct the grinding plates down onto the gem at the angles you are faceting, applying steady, slow pressure.
Polish the stone using a belt sander if you want a true shine on it. Make sure to use the finest-grained plates you can find to remove every last scratch from the emerald. Skip this step if you'd like a matte finish for your emerald.
Oil the stone if you choose to do so. Be aware that although oiling the stone may make it look nicer and brighter, many people consider oiled stone devalued. This is because it makes the stones more reactive to things like cleaning solutions, and it wears off over time, leaving the stone looking worse.