Nagarjuna was the first to use insoluble mercury and Kharpar (antimony) as medicine (agnisah). He discovered five forms of mercury: Red and grey (slake) were good examples, whereas yellow, white, and multicolored (peacock color) required at least 18 treatments (sanskar) before they could be used. Mercury and quicksilver are the subject of a vast amount of post-Nagarjuna literature. The Siddha sect held that parad is Shiva, Mica is Parvati, gandhak is Parvati’s raja, and many fanciful theories were developed. Mercury becomes solid and can be fashioned into a Shiva lingam. They venerated a parad Shiva lingam, named it Raseshwar, and founded the Raseshwarvad religion.
Even in modern times, few Ayurvedic alchemists have made a mercury lingam. Other sects, including Pashupati, Shaiva, Pratbhingya, and Vedics, were drawn to mercury science. Buddhism had sects like Vajrayan (vajra is iron), Lingayan, or Sahajayan, and Mantrayan. They believed that Mantra and Tantra knowledge must be kept secret, but Gorakhnath discussed them, and his chief disciple concluded that this secrecy was merely for show.