Given that artist's quality varnish is created specifically for either acrylic or oil paints, if you varnish a watercolor painting, does it become a mixed media piece of art? Mark Golden (of Golden Paints) says it does, but that's really just an interesting aside in his blog on varnishing a watercolor painting
. He looks at what happens to a watercolor painting when you apply acrylic varnish to it, the reasons why anyone would do this, and warns about it being irreversible!
Read more about varnishing a watercolor
on Mark's blog and in Golden's technical data sheet on varnishing Watercolor
How To Varnish a Painting
Why Varnish an Acrylic or Oil Painting?