Antique pendants come in many shapes and sizes, from beautiful vaseline glass gems to impress, Osler plaffoniers and, not forgetting, a vast array of pretty, coloured pendants. The different colours found in glass shades are made from dropping tiny amounts of a specific metal or compound into the glass when it is molten. This allows for a beautiful array of colours. Some of the most striking antique shades are formed using gold, for cranberry glass, tin oxide to produce milk glass and the most famous and valuable of all, uranium to make vaseline glass.
For a detailed list of oxides, metals and colouring ions which colour glass, see this guide.