The big sticker mandala is finally sealed and ready and leave the house. It took literally months trying to find a varnish that would protect against moisture and UV radiation without discoloring the stickers. I think all the varnishes I tried were reacting with the adhesive somehow, because they made the edges of the stickers look like they were soaked in grease. Ick.
After three failed attempts (on test pieces, of course) I finally found what I was looking for: Liquitex Varnish (acrylic polymer emulsion), which I bought in the matte finish (it also comes in glossy).
The polymer emulsion sealed the collage properly, even holding down some of the sticker edges that had been popping up and it dried totally transparent, while at the same time reducing glare. It was thin and easy to apply with a soft, wide brush, which didn’t leave any brush marks. Look how nice!
But the best thing about this stuff is that unlike all the other coatings I tried, it’s water soluble, which means I could use it indoors without nasty fumes killing my bird and I could wash out the brush with soapy water, not toxic paint thinner. This was a huge bonus, since it would have been impossible to seal this piece outdoors without all kinds of debris and particles landing on it.
Long story short, if you need to seal something you made with stickers or other not-very-absorbent materials, try this stuff. Of course, always try a test first, because it’s impossible to predict how some materials will react.