Aside from the cold pool, there is always the power of suggestion, although the pool is more likely. If you watch them, you'll notice they will become prominent sometimes and hidden others, depending on warmth, physical activity, skin condition (sunburn, tan, irritated, etc), as well as your own thoughts about them. . My concern is why you want this man to show you how he does it. If he's claiming to be a black witch, stay away, just as you'd stay away from someone who would admit, "Hey, I kill things for fun," or "I meddle in peoples' business for fun and try to mess them up." Morality does not go out the window the moment you pick up a staff. I have also found that almost all of these people have limited power, anyway. There are the few that have grown to excel in their arts so fantastically that it takes a powerful will to heal what they've done, but most get caught up in their own tangling spiral. I once thought that the Universe liked to put a cap on these people - now I've learned that they do it themselves. NOT TO MENTION those who say they are "black" and "white" usually have about as much control over the happenings of the universe as a slug.
Even if you did decide to go learn from him and perchance create your own spiral, who is to say he won't harm you?
Crazy Healer Lady
Health and happiness to you!
The purpose of a relationship is not to have another who might complete you, but to have another with whom you might share your completeness. -CWG