Clairvoyance is the ability to see some areas of the astral world. Some human beings, through their spiritual growth, have been able to learn to see frequencies that are not visible to most humans. Often clairvoyance begins with the ability to see ethereal bodies of beings. This is often called “aura reading” although the ethereal body is only a minor part of the aura. Of course observing the ethereal body can be very helpful in disease analysis, however in a way the ethereal body is a mirror image of the physical body and this “see-through” body makes it possible to some humans to see the inner organs and other parts of the ethereal body as if the body was made out of glass.
The ability of clairvoyance can be developed to various degrees and extend past seeing the ethereal body. Parts of the spirit world may be observed, and there is a larger number of humans who are able to see some spirit beings, e.g. souls of humans or other beings that are currently not incarnated, and there are some humans who are able to see other areas of the human aura, mostly the emotional body and in some cases other higher bodies.
Some humans have the strong desire to be able to see such areas. Although it is possible with some special exercises to promote the development of these (extra)sensory perceptions, the spiritual development of the human, and the cleansing and strengthening of the chakras is the only suitable way for the soul to open up the third eye which makes clairvoyance possible. Forcing to open the third eye is something dangerous for the unprepared soul and does not serve spiritual development. Be warned of hallucinogens, these may rip open the third eye with consequences for many incarnations.
Among Native American and other indigenous peoples there has been limited use of hallucinogens for spiritual purposes. Their use was in accord with an older wisdom and at the right dose for prepared persons (e.g. medicine men or shamans) it has usually been without harm. It is then mostly used as an aid to strengthen the clairvoyance ability of the shaman. Be warned of misuse for other purposes and improper use, as this can forcefully open sight into the lowest realms, where there are demons and similar creatures, and may cause very severe harm to the aura.