Some thoughts on layering
To get a better understanding of layering colours in gouache, we’ll look at how some of them behave on light and dark values. In the four swatches, I’ve taken the primaries and laid them on top of the white of the paper, a wash of opaque titanium white, and black.
This desaturation is more obvious when laid over black. Although they were applied in a fairly thin wash, you can see that on their own, the primaries do display some degree of opacity. The main observation that you can take from this is to avoid layering darker values over light paint. Save that tube of Titanium white for the final stages. And when layering lighter colours over darker ones, you may need to sacrifice some vibrancy in favour of opacity. Work in your midtones, then dark areas, and save the highlights for last. OVER BLAC K
In the second sample, you can see that the first wash of Titanium white affects the primaries that are laid on top. Where the two colours overlap, they look duller and slightly more desaturated than when applied directly to the paper.
In the fourth swatch I’ve added about 30 per cent Titanium white to the primaries, and you can see that they automatically have better coverage than before. Unfortunately, this comes at the cost of their saturation. If I were to apply this practically then I’d use a pure hue on the white of the paper, and add Titanium white for better coverage on dark areas.
The three swatches of primaries are at their brightest when laid directly over clean, white paper. Primaries on paper