Optimization of Sapphire [Sapphire Introduction Course 7]

Heat treatment is the most common treatment of sapphires, usually to improve their appearance or color. The earliest records of ruby/sapphire heat treatment can be traced back to 1045 AD. In the writings of Al-Biruni (a Persian scholar), he described the use of a blowpipe to treat corundum gemstones at a temperature of up to 1100 ° C to remove the blue hue of rubies, etc. Some optimization methods will have a great impact on the value of gemstones, such as the lead glass filling or diffusion treatment of sapphires, which will be explicitly named "treated sapphires" in the appraisal conclusion.

In Sri Lanka, the main source of sapphires, there has been a tradition of using heat treatment technology to improve the appearance of gems for hundreds of years. In the 1970s, the development of heat treatment technology for corundum gems, especially for Sri Lankan Goda varieties (Geuda, colorless or milk-colored sapphires), had an important impact on the international gem market.

In 1916, it was reported that dark blue basalt sapphires produced in Queensland, Australia, became lighter in color after heat treatment. Since then, this process has been widely used in dark blue basalt sapphires and continues to this day. As these gems were pushed to the surface of the earth during the formation process, they have already experienced natural heating from the basalt magma inside the earth, so additional artificial heat treatment has become difficult to discover.

In recent decades, as more and more ruby and sapphire deposits have been discovered, more targeted treatment methods have been further developed in order to improve the appearance of more gemstones. This includes the use of more special equipment (such as electric muffle furnaces) and more precise heat treatment parameters (such as controlling the redox environment, temperature and time, etc.). From the end of the 20th century to the 21st century, there are mainly two different types of optimization treatment methods applied to corundum gemstones:

1. Heat, but no additional coloring elements are added, and fluxes are not added to fill or even "heal" the cracks. All methods of optimizing the treatment of gemstones by heating alone have been known as heat treatment according to convention for decades. For example: heat treatment of Geuda sapphires, low-temperature heat treatment of pink sapphires, and Punsiri heat treatment applied to sapphires, etc.

2. Heat and additionally diffuse to add coloring elements to improve color, and/or assist in heating with fluxes to fill or even "heal" the cracks in the gemstone. In these cases, each different method will be specifically described and stated in the appraisal. For example: beryllium-diffused treated corundum gemstones, lead-glass-filled treated rubies, and so on.