First of all it is necessary to try to understand that the Chinese culture has it’s own representations, sometimes radically opposed to the concepts of other cultures. Taoism, and especially alchemy of immortality in Chinese traditions are well-known everywhere, however, I shall dare to say that they have not been perused at all.
Especially it concerns the most ancient stratum of Taoism and so-called the doctrine of shenxian’s (the teaching of shengxian's (taoists, taoists saints)). It’s not surprising because it’s wide-spread even in China. So the achievement of immortality is not a desire to leave the memory about oneself to descendants and not a desire to live on earth forever (and physical immortality and longevity, although considered realistically achievable, but have never been the supreme goal of Taoism), it’s realization of the supreme freedom which lives in every man, although he usually doesn’t know about it. This is described very well in Zhang Bo-duan’s “Chapters of Understanding Truth”. Thus, Taoism is not a philosophy or religion but the Way of Freedom. Of course it’s very difficult to find the essence of Taoism among temporary accretions and distortions, but even nowadays there are people in China who keep that most ancient tradition of Taoism.
Taoist alchemy is the Doctrine about finding THE UNITY. And it is not about physical or life consciousness (as they understand the spirit), but the achievement of the particular state which is the Highest Possible Human Achievement In the Realm of Spirit. The purpose of Immortality in Taoist alchemy is more aimed at the spiritual immortality rather than the physical immortality. In practice there are certain stages which are characterized not by phenomenon of qigong but by physiological changes and transformations (notably 人 仙, 地 仙, 神仙, 天仙, 金 仙 and some others). Not all schools of Taoism call the same levels with identical names. It’s important to emphasize that the Chinese Spirit has nothing to do with the concept of consciousness which is expressed in hieroglyph 神.
As is known, in past the Alchemy was known as NEIDAN and WAIDAN (which is usually translated as the internal and the external alchemy). The DAN hieroglyph denotes a crucible in which the melting occurs. However, only few people know (and Taoists insist on this) that this doctrine existed from time immemorial and is known in China since at least Huangdi. This teaching is called HuangLaoSyue – i.e. teaching Huangdi - Laozi. This doctrine has also other names. And the terms NEIDAN and WAIDAN appeared much later, at the beginning of our era. Actually, alchemy can only be named WAIDAN as the doctrine of external melted elixir. The internal alchemy (which in science is considered as derivative from external one) had higher and ancient status in tradition. They call it Alchemy because of more accustomed standards rather than meaning.
Let's stop on the classification in more detail:
1. Phantom-immortal or ghost-immortal - Gui Xian ( 鬼仙 )
Gui Xian. Literally - the immortal among devils or the immortal devil. It was believed that this achievement is a characteristic of shamanic practices, the late Chan Buddhism, the pseudo-Taoism, different meditations. Withdrawal of Yin spirit in a state of no breath and palpitation. The practitioner remains mortal, despite the practice of spirit withdrawal and possible capabilities. Moreover, he may not be reborn after his death and stay a ghost forever. This was not practiced in Taoism, it was forbidden (meaning the serious study, not just jingzuo).
2. Human immortal or immortal among people – Ren Xian ( 人仙 )
Actually – one is not immortal. Moreover, each man in his life passes through this period. This is the age of majority, the peak of the blossoming physiology. During this period people have especially sublime state (in a sense of fullness, activeness). If to start practicing alchemy in this period, it will be possible to quickly complete the second stage - the Earth immortal. If the time has passed and the energy dissipated, the old age and infirmity had come, it is necessary to return the body to this stage of physiology. Otherwise, it’s impossible to move on. Thus we see that this still is not immortality, but only achievement a high fullness of the primordial energy, ie Ming.
3. Earth immortal – De Xian ( 地仙 )
This is something that everyone understands as immortality - the immortality of living of physical body on Earth. Although such body can exist indefinitely on Earth, it can be destroyed by external destruction. Therefore, even this achievement was not considered high and all practitioners were seeking to rise further, considering it only as an intermediate stage. It is necessary to add that this achievement - is the ultimate goal of the external alchemy.
However, in the previous phase and at this stage it is possible to perfect various qualities of your level, although it’s not the main way but the side paths. At this stage Ming merges with Xing in a one whole which is why the immortality is possible. Here is comes some similarity to the thermonuclear eternal engine in the body amidst Earth conditions. That’s why there are such capabilities.
From this stage the achievements are irreversible in a way of returning transformation (the exception is the phase of Jen Xian where it’s easy to become an ordinary person again after having wasted Ming). But if due to external conditions or because of the body destruction the practice is not completed, it may be needed to revert to the previous level.
4. Spiritual immortal – Shen Xian ( 神仙 )
Spiritual fetus - Yanshen goes out of a human head (is born in the spiritual world) but it still needs to be educated and developed. That looks like a mother (body) takes care of her child (spirit). After its strengthening and implementation of this phase this spirit can move anywhere in the Universe - primarily to understand its structure and subsequently for execution of spiritual work. It’s impossible to kill it, it’s immortal. But there’s still a body which requires attention. At a certain stage of its development the yang spirit Yanshen gets the opportunity to divide, reproducing the same doubles. Their number gradually can grow to a huge multiple. They can do various spiritual works in different worlds. That is when the complete understanding of the Universe laws and the sense of the further development come. If a practitioner wishes, this phase can be stretched to a very long time. For example, it is possible to sit in a cave for a millennium and to practice in spiritual bodies.
5. Heaven immortal – Tian Xian ( 天仙 )
Let me remind you that even the previous stage can be stretched on endlessly. But the immortal spirit still has not- transformed body. Therefore there remains the possibility of realization of the highest stage which is possible on Earth according to alchemy - the transformation of this body in the body of light. This is the most difficult task because it requires about 9 -10 years of immobility. It should be provided either by faithful pupils and adherents, The Teacher, or by concealment by having immured in a cave according to certain rules. After its implementation the body and the spirit merge together in the "body" of light and when the achiever leaves the world nothing is left (except for remaining things as in case of with Bodhidharma’s shoe). If due to some reasons the practitioner does not reach the highest stage, he may either himself at his will or under certain circumstances "get rid of the corpse." Depending of the achieved level his left body may not be susceptible to decay but self-mummify or even burn from the inner fire.
This scheme is based on the study of tracts on the one hand and precepts of the Teacher on the other.