For the kind of illustration I’m interested in, the style requires some very smooth, matte, single-color backgrounds. Traditionally with watercolor people would do large washes of 2 to 3 colors (e.g. for a sky), but for the kind of illustration I do, which has a lot of details, traditional washes are not a way to go. I could not find a single article or youtube video that shows how to do large, non-square areas of matte, smooth painting, so after a lot of tries, I found this technique:
– Get some paint on a plastic palette. About the size of a raisin for a small area.
– On a separate palette hole, add thrice as much water as the raisin size of paint above.
– Use a size 8 “pointed-round” soft brush (Kolinsky sounds good).
– Mix the paint with some Titanium White.
– With the tip of the brush, get some paint (just a little bit, maybe about 1/6th of it), and mix it well with the water. It will create a very pale color, but it will still have a color.
– Strain away as much water as possible from the brush. It should not be full of water when you lay it on paper.
– Start laying the pale color on your paper. Use as large brush strokes as possible, and move the pools of paint towards a single direction.
– Let it dry for a minute or so.
– Add 2/6ths of the paint (basically, double as much as before), on a bit more water than before (maybe about 1.5 times as much as before).
– Mix well, strain the brush, and paint over, the same way as before.
– Let it dry for 3 minutes or so.
– Add the rest of the paint to about 2x more water as in the beginning, strain the brush, paint over again. The consistency should be that of a melted ice cream.
– Let it dry for 5 minutes before you decide if you need yet another hand on top, or add details on it.
That’s it. Basically, you need multiple layers to get a smooth, matte finish.
Another way to do it with gouache, is to lay gesso+medium in the paper before painting, just as if you were using acrylics. The 2-3 gesso hands would then serve the same way as the multiple hands of paint. Personally, I prefer the first method.