A talisman is a symbol representing a certain force, or combination of forces, depicted upon a suitable substance and magnetised by ritual. It can be made from anything which will retain magnetism; metals, precious stones or parchment are usually employed; paper is less effective unless it be enclosed in a metal case. Water and oil can be effectually magnetised but soon lose their potency. A talisman is made by invoking the requisite force, as already described, and then concentrating it upon the prepared object, which is placed ready upon the altar before the evocation begins.