Setting

Invisible setting is not a retouch that hides prongs. A continuous V-groove under the girdle of corundum takes a metal rail measured in fractions of a millimetre, stone against stone, with no visible wall. Light enters the table and leaves at the side, without a prong shadow cutting the colour. Jade, pearl, opal and copper tourmaline are not asked to perform it. Where a shadowless join is not honest, short prongs are used, and their number is said aloud.