The processing of metallic mercury into the form of a mercury sulphide ash, called tsotel (btso thal), is considered the most refined pharmacological technique known in Tibetan medicine. This ash provides the base material for many of the popular “precious pills” (rin chen ril bu), which are considered essential by Tibetan physicians to treat severe diseases. Making tsotel and precious pills in Tibet’s past were rare and expensive events. The Chinese take-over of Tibet in the 1950s, followed by the successive reforms, including the Cultural Revolution (1966–1976), affected the opportunities to transmit the knowledge and practice of making tsotel. In this article, I discuss two Tibetan physicians, Tenzin Chödrak (1924–2001) and Troru Tsenam (1926–2004), both of whom spent many years in Chinese prisons and labour camps, and their role in the transmission of the tsotel practice in a labour camp in 1977, contextualising these events with tsotel practices in Central and South Tibet in preceding decades. Based on two contemporary biographies, their descriptions of making tsotel will be analysed as well as the ways in which the biographies depicted these events. I argue that the ways of writing about these tsotel events in the physicians’ biographies, while silencing certain lines of knowledge transmission, established an authoritative lineage of this practice. Both physicians had a decisive impact on the continuation of the lineage and the manufacturing of tsotel and precious pills from the 1980s onwards in both India and the People’s Republic of China (PRC).