Before setting colored stones wash your hands, and clean off your bench top, bench pin, and lap tray. Metal filings and abrasive particles on your bench and hands can scratch soft stones during setting.
When setting colored stones, use a head or crown that is slightly larger than the head you would set the same size diamond. This larger size is needed to accommodate the larger pavilion on color stones.
When setting colored stones with an uneven pavilion in clusters or as side stones, set the thicker portion to the outside of the mounting where it will receive more abuse. If the stone is set with the thinner edge to the outside, it maybe chipped while wearing.
Test your pumice wheels and other abrasive wheels on a piece of glass. If they do not abrade the glass, they will not scratch most faceted colored stones, and would be safe to use cleaning up the prongs. Glass is around 5 ½ on the Mohs scale, which is softer than most faceted colored stones. Although these wheels will not scratch harder gemstones, you still must use caution as the wheel may chip the facet lines of fragile stones.
When setting colored stones, it is extremely important to place the stone in the mounting in exactly the same position each time you test fit the stone while cutting the seat. The reason is due to the fact that most colored stones are cut irregularly. To assist you in this placement, draw a line on the crown of the stone with a fine tip marker. Then line-up this mark with a distinctive design element of the mounting, a similar mark with a felt tip marker on the mounting, or a mark made on the holder holding the mounting (such as a deep file mark filed into your ring clamp). When finished setting, any remaining ink can be removed with alcohol.