Synthetics are crystalline materials, which have been formed artificially (e.g. in a laboratory) and which possess the same (or nearly the same) crystal structure and chemical composition as their natural counterpart. As a consequence synthetic materials show similar or the same physical properties than the natural material. A synthetic material has to be disclosed on all levels of the trade (e.g. synthetic emerald or synthetic diamond). Synthetic ruby, sapphire and spinel have been around since the beginning of the 20th century (Verneuil method). Synthetic emeralds and synthetic diamonds since the 1950s. There are different methods used to synthesise gemstones, depending on the crystal structure and chemistry and cost. These include flame fusion, flux melt, hydrothermal, skull melting, CVD and HPHT. The proper disclosure of synthetic stones is vital for the trade and to maintain consumer confidence.