While you can varnish watercolor paper, it is a little different than varnishing canvas. It still needs to be framed behind glass to protect it from water and humidity, but a varnish can help prevent fading. You want to get a matte spray varnish. I use the matte spray varnish by Golden. It’s archival and offers UV protection. There’s not much of point in using a varnish that isn’t archival.
With coffee and tea, you want to varnish as soon as you can because it’s not just contact with light that causes it to fade, but also contact with oxygen. It needs to be completely dry first, but after that, varnish it. Watercolor can wait a bit if you keep it out of the light. Even if you get acid-free paper, there’s still acid in the coffee and tea.
Hopefully that’s helpful. If you try it out, let me know how it goes. Also if you have any questions, leave those in the comments too!
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