He was talking about a work he did with paper, acrylic paint on canvas. Many artists like to use several meduims on canvas and don't know how to make the work look smooth, making it seem like a single layer with lots of dimensions.
I use a vanish on most of these type works for this effect, I like to use a very glossy look. You can use many varnishes that are used on wood. Paper is a wood product. Most of these varnishes are safe for acrylic and oil paint too. Ask for a clear, glossy, wood type varnish or finish at your local Home Depot or paint store for a cost effective product. Home Depot here lets me see samples of what the vanish will look like dry. You can always ask for the same sort of vanish at some local art stores too, but you will pay a premium price for it there.