How do you get that surfboard finish so popular on paintings? You know, that super clear, glossy, smooth top coat. The best results can be obtained using commercial resins. They come in two parts – a resin and hardener. They are, however, very toxic to work with. I prefer to use acrylic non-toxic fine artist alternatives that may not look as perfect, but will also last without yellowing or cracking.
My favorite technique is to lay the painting flat and very level, and propped up on containers to get it lifted off the table or floor. By the way, it is easier to work with rigid surfaces like panels. If you are using a stretched canvas then you need to prop up the center of the canvas to keep it from sinking downward while laying flat. I then pour Golden's GAC800 without diluting it with water onto the painting’s surface. I spread it out evenly with a plasterer’s knife, and then immediately spray lightly with isopropyl alcohol to eliminate any bubbles. This takes a day or two to dry but has a smooth glossy finish.
The GAC800 is the only pourable acrylic that I know of that can be poured in deep layers without crevising. So you can also take duct tape and tape around the outside edges of the painting creating a wall that stands out from the top surface of the painting. By applying a small amount of a thick acrylic gel where the tape and painting meet you can keep the pour from later leaking out. While the gel is still wet pour the GAC800 into the pool or well that’s created by the tape. You can get a very thick poured layer this way. The thicker the pour, the longer you need to keep the painting level and flat while drying – which may take weeks if it’s more than an inch thick. When the GAC800 is used thickly it will appear slightly yellow and cloudy, not really visible in a pour with no walls or duct tape, and is favored by artists that like the "wax" or encaustic appearance.
If you don't like the cloudy look of GAC800 you can use other pourable products but you can't pour them thickly in one pour, or they might crevice as they dry. Instead pour several thin layers. My favorites for these are Golden's Clear Tar Gel and Self Leveling Gel.