Don’t be fooled by this old sales pitch. Almost all gemstones common in fine jewelry will cut glass. Why? Diamond is a 10 on the mohs hardness scale. Glass has a mohs hardness of only 6.5. Since most gemstones used in jewelry (i.e., sapphire, ruby, topaz, quartz, citrine, amethyst) have a hardness above 6.5 they will all cut glass. And yes, almost all simulated diamonds including Russian Brilliants will cut glass.