I get dozens of requests to describe how I varnish my watercolor paintings, so instead of typing the info over and over again, I've decided to post it here on my website. I glue my paper to a wood or MDF panel, varnish with acrylic spray. I don't need to use glass or matting.
*** Experiment on a painting you don't care about the first time you try varnishing your watercolor***
1/8 inch or 1/4 inch birch sanded plywood or Medium Density Fiberboard (MDF) from Home Depot, cut to size.
Arches 300 pound, cold pressed watercolor paper
Liquitex matte acrylic medium (for glue)
Golden UV resistant spray varnish (to fix the finished painting)
Either Golden brand or Liquitex brush on varnish, (Gloss) for final varnish.
I cut the board into the size I want with a jigsaw. I cut the board into sizes that correspond to standard frame sizes - such as 8x10, 9x12, 11x14, 12x16 and so on. If you don't want to use a saw, you can order pre-cut boards in these sizes from most art supply catalogs. I don't know the names of the brands, but I have seen them listed at the major art supply companies.
I cut the watercolor paper so that it's 1/8 inch larger than the board/panel.
Instead of household glue, I use acrylic matte medium as a glue because it's archival - meaning it is acid free and won't rot the paper.
I apply acrylic matte medium with a brush to the back side of the paper and to the panel. Then I position the paper (glue side down) to the panel (glue side) and press firmly, especially around the edges of the paper where it tends to curl up. Then I place the paper side down onto a clean, flat surface and stack a bunch of heavy books on the paper/panel - leaving it overnight, or for several hours so that the paper is firmly glued to the panel.
When my painting is finished, I use Golden spray UV resistant varnish to "fix" the watercolor so that it doesn't run later when I apply the brush on varnish. (two light coats)...You'll need to use this spray outdoors because it's toxic to inhale. When the spray is completely dry, (usually a few hours).
Then I add a tiny bit of water to Liquitex Acrylic Gloss varnish and brush it on the watercolor painting. I don't brush it too long because I run the risk of the varnish getting milkly. As I said, try this all on a painting you don't care about - just in case you ruin it.
If you don't want to run the risk of using brush on varnish, you can (instead) spray a coat or two of gloss acrylic varnish on your painting. One watercolorist I know uses several light coats of Kmar varnish as his only varnish. I've tried this myself and it works very well.
That's about it! It takes a little practice - trial and error, so don't do this on a cherished watercolor on your first try!
When it's completely dry, pop the paper/panel into a frame (I use the kind of frames oil painters use, which are a little wider than typical watercolor frames) I don't need glass or matting, which saves me money.