Hi Lollo. You have the process right. As with liquid white, it takes a very thin coat to do the job. The fingerprint test doesn't really work since it's clear. Once you have the canvas covered, you can wipe it down with paper towel. Then smooth it out with a clean two inch brush. I like the blue shop towels for this. They cost a little more, but they don't leave fibers on the canvas. Don't worry about taking too much clear off, you'd really have to scrub to do that.
As for the liquid black, Bob only used it a handful of times. I can't think of any examples right off hand.