When we paint with gouache, previously laid layers of paint will get re-wet, and dissolve again, mixing into and strongly impacting (usually, for the worse) whatever we are trying to create on top.
I know one advice is applying layers in a specific order: starting with very diluted, and using less and less diluted subsequent layers: starting with "watery" and progressing towards "buttery" consistency.
Yet I'm afraid even this layering discipline won't help sufficiently when I'm:
- trying to use an underpainting
- trying to create a gradient (I mean "blending") (which, with gouache, is challenging already in itself) on top of a previously laid layer of a gradient.
Casein? Very close, but...
I know James Gurney likes to use casein, which will not dissolve once it dried. He uses it as underpainting under gouache pieces, and for entire works too.
But: casein does not seem to be widely available in my region (and I'm not big into online ordering paints), and anyways I'm also discouraged by the challenges that its organic nature imposes on handling it (like its quite short shelf-life). So I would rather look elsewhere.
What other approach can one take?
What other thing could I do, what additional material(s) should I bring in to achieve my above introduced goals?
I am interested in solutions that:
- do not compromise the archivalness of the finished works: I wish uncompromised lightfastness (as good as the original paints'), and reliable, long-term adhesion to the carrier material (paper, gesso'd panel, etc.)
- (preferably) leave the painting's surface similar in character to the original gouache's: I might still would like to apply some color pencil strokes on top, as part of the final steps