The Dzogchen teachings are considered the pinnacle of Buddhist meditation practices, and often the practices are centered around working directly with the nature of the five elements. The five element practices that Nyala Pema Dudul revealed as terma was called "Sky-Encompassing Self-Liberation" (Kha'-Khyab Rang-Drol in Tibetan), and within that series of teachings there is a practice of alchemy called "Chulen of the Three Dimensions." The picture below is of the cave where he revealed this terma.
Chulen literally means "taking the substance." There are many types of chulen that have various applications. Tsi dang contains eight ingredients which work together to strengthen and coordinate the function of the major organs. Its main effect is physical health and youthfulness. Another type of chulen is called rotsa, which is used specifically to strengthen and balance energy; so there are many different kinds of chulen traditions and medicines.
In the contemplation tradition of chulen, the pills are used in conjunction with meditations and yoga in order to recognize awareness as the pure nature of the elements. The practice is a gradual process where the practitioner weans himself from eating solid food, and attainment of the practice is the development of the ability to subsist on the pure essence of the elements themselves. At that point, the practitioner no longer has to eat anything.
The teaching instructs the practitioner on the preparation of medicinal pills, and the method of visualization, breathing and yogic techniques to reintegrate the practitioner's inner and outer experience of the elements back into its natural state. As Namkhai Norbu writes, "Chu is the essential substance of the elements: it maintains the physical body and, if our energy is uncoordinated, it co-ordinates it, if it is weak, it reinforces it. Therefore, chudlen is useful, above all, to harmonize energy and develop clarity...The Body of Light (Jalu) can manifest when the principles of Dzogchen are combined with Chulen." The terma text itself mentions that when the great saint Yeshe Tsogyal asked Guru Padmasambhava for these teachings, he replied, "Listen. There are many methods to achieve total realization, but in particular, there is the Chulen of the Three Dimensions, which embodies infinite qualifications." In Drubje Pema Dudul's biography, it is said that he practiced Chulen with a little solid food for the first three years, Chulen of medicinal pills for the next three years, and Chulen of absorbing the essence of the elements directly from space for the final three years of his retreat. At the conclusion of his nine year retreat he had attained full enlightenment as his teacher the Mahasiddha Choying Rangdrol had predicted.
When Drubje Pema Dudul knew his time was near, he called all of his students back to the area where he lived, and after giving them each his heart advice and practicing the Feast Offering with them, he had them follow him up a mountain, where he set up a small tent and asked them to sew the door shut. With the instructions that they should practice the Feast Offering together for a week before checking on him, they witnessed numerous rainbows appear over the mountain and the surrounding area. When they returned to the spot where his tent stood, they found it still sewn shut; opening it, they found his body had disappeared. His meditation belt and cloak were in a heap, within which they found all of his hair and twenty nails from his hands and feet. This picture is of the shrine built over the spot where he manifested the Rainbow Body.
Drubje Pema Dudul's lineage continues through many masters, including Chogyal Namkhai Norbu, Wangdor Rinpoche, as well as Tulku Serdo Rinpoche, Khandro Sherab Lhamo, and Lama Pema Karma.
Read more at :http://www.tealchemy.org/what/alchemists/index.html