Chanthaburi gem market

Chanthaburi, about four hours' drive south-east of Bangkok near the Cambodian border, has been Thailand's ruby and sapphire town for well over a century. Its own mines and those across the border are now largely worked out, but the trade stayed: rough arrives from East Africa, Madagascar and Sri Lanka to be heated, cut and sold, and much of the world's heated sapphire has passed through local furnaces.

What you find

Mostly corundum: blue, yellow and fancy sapphire and ruby, rough and cut, in every quality from commercial parcels to fine single stones. Spinel, garnet, zircon, tourmaline and other coloured stones are traded too. Cutting workshops and heating specialists work in the streets around the market.

How trading works

The market fills Si Chan Road (Trok Kachang) and its side lanes from Friday to Sunday, busiest on Saturday morning. Sellers carry parcels in folded papers; buyers, many of them from Sri Lanka, Africa and South Asia, sit at tables in the dealers' offices along the street and are brought stones to examine. Prices are agreed by bargaining, often through a broker. On weekdays the street is quiet and most trading happens in offices.

Visiting and buying safely

• Bring a loupe, a torch and patience: the custom is to look at many papers and buy few.
• Heat treatment is the norm for corundum here; other treatments (lead-glass filling, beryllium diffusion) are not always disclosed. Buy important stones subject to a report from a recognised laboratory.
• Thailand allows gems to be exported freely, but check the import rules of your own country before you travel.