It is very similar to the Sabatier effect in photography. I won't describe it here, too heavy. It is a way of producing a thin line of white between two black bodies. The result looks like a negative line drawing. Impressive, but hardly worth the six hours it took me to produce.
What I think he is saying, is that lacquer applied onto wet lacquer, will run upto the previous coat, but not quite reaching it, leaving a rim of white. A good application for painting the eyes, with a very thin white rim.
The fish will be well impressed and will select your piece of plastic over the real thing, any day!