MITRA Forum Question Details

I don't think there would be serious problems with acrylic over light watercolor wash, but gouache applied over acrylic usually beads up and cracks as it dries. The typical result of painting acrylic over a soluble layer like gouache is a crazed paint film, probably with weak attachment. The entire stack would likely remain water soluble due to the gouache component.

There is the difference between water-soluble paints (watercolor, gouache, distemper, etc.) these are diluted with water and are resoluble or at least potentially dissolvable, with later applications of water. Then there are water-diluteable paints that dry to be water insoluble (acrylic dispersion, vinyl dispersion, egg tempera, various oil in water temperas, and to a lesser extent, casein.)

Understanding the qualities, solubility, and inherent brittleness of these components can afford a plethora of effects.

In your scenario, the acrylic dispersion would likely partially or completely dissolve or incorporate the watercolor into its layer.  This may or may not be desirable depending on your aesthetic aims. One could apply a spray acrylic varnish or size to prevent the superimposed acrylic dispersion paints from disturbing the watercolor.

I would worry about the adhesion of gouache to an acrylic dispersion layer of any thickness or gloss. Additionally, gouache is a rather brittle medium. In general, it is best to keep ridged and brittle layer at the bottom of the stratigraphy. Again, the gouache would be dissolved by the subsequent acrylic dispersion paint unless the gouache was fixed in some manner, preferably with an acrylic solution fixative or varnish.

Finally, just as a word of caution, it is generally best to avoid complex mixtures and layering of disparate paints unless that is necessary for your final effect. The chance for failure increases with increasingly complex layering.