Purification is the casting out of negativity, "evil" influences, etc. It is usually performed when a sense of tension or uneasiness is felt in a house, particularly if several people notice it. It is always performed just prior to moving into a new home or apartment, to be sure that no vibrations are left behind from the last tenants. Then again, some magicians perform a purification ceremony every three months to keep the home harmonious and pleasant.
The best time to perform purification ceremonies is during the waning moon. A purification is a minor form of exorcism. Be absolutely certain that you are alone in the house or apartment. After your bath and anointing dress in a white robe or clothes (you'll be leaving the house halfway through the ritual, so dress accordingly). Open all windows, cover all food, remove all pets including cats, dogs, reptiles, birds, even fish. There are to be no living things in the house save yourself.
If you are doing the ritual at a friends house, be sure that these preparations are carried out, and keep your friend out of the house. Take your bath and do your anointing directly before going to the house that needs purification, if it is not your own home.
Light the twin candles on the white altar cloth and set a quantity of the following incense alight in the censer, (again, if at someone else's home, set up a small altar there):
Bay, avens, mugwort, yarrow, rosemary, St. John's Wort, angelica, basil, juniper berries - equal parts of each. Powder and mix in the mortar and pestle.
While the incense is smoking in the censer take several garlic cloves, one for each room in the house (including attics, garages, basements, etc.). Peel the outer skin off the garlic and place one in each room, in the center of the floor. If you have very bad feelings about one room in particular place one peeled clove of garlic in each corner of that room.
Now, add more incense to the censer and carry it around with you, going from room to room in the house, thoroughly censing that area. If you have a swinging censer, swing the bowl in a counter-clockwise direction, which is the direction of banishing, of clearing. Clockwise is the direction of invocation.
When finished, (don't forget attics, etc.) add more incense to the censer and place it on a length of aluminum foil, in the center of the house on the floor. Leave the building (stand outside, sit on the front porch, in the car, whatever) for about thirteen minutes. (Wait until you feel it is time to go back in.)
Once back inside, gather up the garlic cloves, without touching them, put them in a plastic bag and put it in the trash. Leave the candles burning for the rest of the evening. You can burn a little frankincense to purify the atmosphere. But, the purification incense should never be burned while people are in the house.
By Scott Cunningham, Magical Herbalism