Q: Is there a sealer that can be applied to a watercolor painting so that it can be framed and displayed with a glass cover?
A: I would suggest using Lascaux Fine Art Fixative. It
protects paintings from UV rays and prevents yellowing. It will protect
most media—including pastels, graphite, charcoal, crayon, ink, gouache,
and watercolor. Do not use it with oil paints.