Antique glass and crystal: how to spot a good piece

Crystal contains lead: it is heavier than it looks and rings for a long time when you brush its rim. Ordinary glass gives a dull sound that dies at once.

Turn the piece over: a rough disc or slight crater at the centre of the foot — the pontil mark — indicates blowing on the rod. On nineteenth-century production this pontil is often polished, but stays visible in raking light.

Cutting is read with a fingertip. Wheel-cutting leaves crisp edges and very slight variations in depth; a moulded piece shows rounded angles and vertical seams.

Finally, be wary of a service that is too perfectly uniform: large antique sets almost always show small differences in height and tint.