Sardonyx is a kind of agate whose bands are straight and parallel. Like agate, it is often dyed to enhance or change its colours. The colouring of agate was an art practised early by the Romans, but it reached its perfection in the 1820s in Oberstein, Germany. This town is still the world centre for the finest cutting and dyeing of agate. Although the details of the process remain a trade secret.
The stone can be traced back four thousand years to ancient Egypt. For most of its history, this stone has been used to create onaments. In ancient Rome, women wore sardonyx necklaces with pendants of Venus, hoping to harness the power of the goddess of love. It was also common for soldiers to wear sardonyx rings and carvings with images of the war god Mars in battle as a means of protection. Sardonyx was also a popular stone for Roman seals and signet rings, used to engrave wax emblems on official documents because hot wax does not adhere to this stone.