What is spirit materialization?

Are you aware that certain spirits are now materialising themselves, so that they can be felt, seen and heard to speak?

I am not aware of this, but I do not consider it impossible. You will notice, however, that those spirits who do so are likely to be of a low order and they manage to produce such manifestations at the expense of spirits in the body. 

We could accomplish these things too, but it would be injurious to the medium. 

It is no more wonderful for us to appear in the materialised form than it is for our Indian friends to produce those perfumes with which you have so often been favoured—the one is as much matter as the other. 

The Spirits you refer to have for a long time manifested in such a way. 

We have one here of the same order—a rough gem—I mean him whom you know as Jok. He could do what the spirits you refer to are doing, but the Indian Spirits would not allow him—they do not think it right.

—Hafed, Prince of Persia