Since the 15th century, Chanthaburi ("city of the moon") has been known to Western travellers for its abundance of gemstones. As a trading city its history dates back to the Khmer Empire in the 9th century. Along with Bangkok, Chantaburi is world-renowned as a gem centre, and for its skilled gem cutters. The gemstones- mainly rubies and sapphires , with associated deposits of zircon, spinel and garnet - are found in alluvial deposits either on the surface or up to 6 m (20 ft) underground . Although rubies and sapphires are now over-mined around Chanthaburi , farmers have previously found gemstones while ploughing . Over 70 percent of the world's rubies have come from Thailand.
Examining gemstones in the host rock helps formulate the correct cutting plan. This ensures the best yield and stone shapes are obtained.
Simple grinding wheels are often used in small business, which are commonly run from the owner's home. More sophisticated operations use modern equipment such as diamond saws.
Thai workers have a worldwide reputation for their skill and dexterity in facetting (precisely cutting) gemstones, often using simple equipment and judging angles by eyes. A modern facetting machine may use a diamond blade or laser to improve speed and accuracy . After cutting , the stones are sorted and graded by size and quality , with quality being determined by sparkle, colour, brilliance and the presence or absence of imperfections.
Modern facetting equipment used to cut gemstones.
Most gem buyers prefer to buy gems "in the rough", using their expertise to judge the potential of the uncut material. Later the buyers arrange that cutting of the stones, often in their own workshops. Untrained buyers should beware potential scams
Bargaining in gem-mining towns such as Bo Rai is common pratice . Since opinions differ as to the potential of rough material and the quality of cut stones , bargaining is hard but good natured.
Designing and making jewellery from gems demands a delicate touch and a keen eye, qualities renowned in Thai craftsmen and women. Most jewellery is made to high-light the beauty of the gems.