The art of making eyeglasses was perfected by the craftsmen in the island of Murano in Venice. These craftsmen came to be known as the Cristallieri. They used quartz or rock crystals as the main material for making these glasses until the discovery of ordinary glass (Cristallum). Very soon craftsmen guilds were created in Venice which laid out certain regulations for making and selling glasses made from Cristallum. The new rules prohibited Cristallieri from selling these ordinary glass products under the guise of exotic crystals. The organization also adopted a term for these “discs for the eyes” by calling them "vetri da occhi".