The development of Rasashastra as an independent branch started since eight or ninth century A.D. and then onwards number of ancient scholars have contributed in its development.

According to Ayurveda, 'Parad' (Mercury) and 'Gandhak’ (Sulphur) are the most important minerals as they represent Lord Shiva and Goddess Parvati, the deities of purity and strength, respectively.

Both mercury and sulphur could be toxic separately, but blended together, they form black amalgam known as Kajjali, which is relatively safe and makes an ideal base for most of the uparasa preparations. Kajjali is claimed to exert potentating effect on the properties of other drugs and makes them easily assimilate in body tissues. 

Ayurvedic chemists have evolved various procedures like sublimation, oven treatment, controlled heat incineration, grinding, mixing, churning etc. to inculcate the therapeutic properties in the minerals for which many specific types of yantras (instruments) are designed.

When it comes to using any metal, mineral or a natural product directly or as a formulation, the alchemic scientists (Raja Siddhas) state that, barring a few exceptions everything should be purified/detoxified first (Shodhana) and then must be converted into bhasma (ash). This is achieved by controlled/sustained heat incineration again and again, as many times as possible.