To make lead crystal, lead oxide is melted at around 1400°C with silica sand and other organic compounds. To be called 'crystal' the materials used must contain a minimum of 24% lead or other metallic oxide. It is this which gives the crystal its brilliant sparkle and lustre.
Crystal items have the highest clarity and brilliance, while the high lead content gives them a satisfying weighty feel. Although relatively strong, crystal is soft to the touch and easily worked. Hence it can be easily decorated by 'cutting' and engraving or formed into elegant shapes and glasses with fine walls.
If looked after properly, crystal should last a lifetime. When buying, consider the style of glass, the appearance of the crystal and the function.