[Steve Ellsworth]

The air pressure varies by the shape of the tip - flat ball point, how deep i want it to go, what i am trying to accomplish and of course the type of metal. Some being softer than others.
Most people think of stippling as just puinching a lot of tiny holes in the metal to cover up mistakes or get some kind of artistic effect, I use a wide variety of shapes and sizes (small) to chase the metal.

So it varies and it's an experimentation process. I always do it under magnification to start with to get most of the areas covered and then switch to a visor and move things around to see how the metal needs to be worked to make things look consistant under differnt lighting. In that respect it's a lot like doing bullino.

Regardless of the pressure you have to keep theangle of attack consistant or things get weird

hope that helps