Quartz is a special kind of glass made from quartz sand with a very high purity of silicon dioxide. It can be processed into melting crucibles with different production methods and therefore be transparent or translucent. For the precious metal industry translucent crucibles are more relevant.
The temperature range goes up to 1500 °C, beyond that point the material softens slowly. In combination with a support crucible (e.g. Zirconia) around the quartz crucible the temperature range can be raised up to 1900 °C, so platinum group metals can also be melted in quartz.
The high chemical purity prevents any unintended chemical reactions with the product. An excellent thermal shock resistance is beneficial to more steep heating curves, enabling fast heating and fast cooling.
A homogeneous glazed surface on the inside enables smallest possible pore sizes and smallest inclusions of foreign material into the precious metal. This way the best possible surface quality can be achieved, which is especially beneficial to products delivered into the investment bullion, electronics and medical markets. Furthermore, translucent quartz is a good heat isolator, but not inductive itself. Therefore, in use with inductive furnaces the heat will stay inside the crucible much longer and built up quicker, so time and energy costs can be lowered in this application.
Quartz is highly resistant to most acids, so processing with e.g. sulphuric acid and hot chlorination is possible in quartz crucibles. On the downside quartz is difficult to process, so not all sizes and geometries can be produced and the products are rather in the higher in price.