Glass is a terrible diamond simulant. Even very specialised lead crystal glass has far lower refraction and dispersion than diamond, giving a dull gemstone with

Glass is a terrible diamond simulant. Even very specialised lead crystal glass has far lower refraction and dispersion than diamond, giving a dull gemstone with little fire. It's also far softer than diamond and quickly becomes dull and scratched with wear. Synthetic moissanite (silicon carbide) is optically superior to diamond at drastically lower cost. Even to an untrained eye, moissanite has visibly superior brightness and fire. Cubic zirconia is optically comparable to diamond and ludicrously cheap. Moissanite is only marginally softer than diamond and cubic zirconia is comparable in hardness to topaz, emerald and spinel.