Stretching your watercolor paper has certain aesthetic advantages.
You'll end up with a perfectly flat surface on which to work. This surface will stay relatively flat as you work and the finished painting will dry perfectly flat. The only disadvantage is that it takes some effort and dedication to do it consistently.
Any paper of less than #300 weight is bound to warp according to the amount of water absorbed in the painting process. Synthetic papers generally do not warp at all. Watercolor paper in prepared blocks will dry flat also, if left on the block to dry
I use 140 lb paper for the paintings that I sell on ebay so I almost always stretch it.
I find 90 lb. paper is too flimsy for serious watercolor work. When I use 300 lb. paper it doesn't require stretching, but it is expensive so I use the 140 most of the time but love to paint on 300 lb when I am really working on a large painting I use 300 or 200 lb paper.
When Stretching watercolor paper I allow 1” for gumstrip all the way round the paper. Fill a large sink or bath with water and submerge the paper, rolling/folding it as necessary. Do not crease it. A heavy paper [300lb/640gsm] must soak for 15-20 mins, a lightweight [90lb/190gsm] one needs only 4-5 minutes.
I find that soaking the paper makes it nicely receptive to washes.
However, if you are not using wet washes over broad areas, you may
press the paper, right side up, against a smooth, nonabsorbent board (gator board, plywood sealed with varnish or a piece of plexiglas). The surface tension of the wet paper will cause it to remain fixed to the board for 5 to 10 min, I then wipe off excess water and tape it to the board with masking tape. Some artist like to staple it but I like the white edge that taping give the painting.
About This Painting: If you’re after rich, dripping , pure color and brilliant lights, then you might consider trying this dark-to-light approach to watercolor. This system calls for painting the darkest darks first, sliding into the middle values, and saving the lights as stark white paper. In addition, there’s no need to premix paints. Just lay in pure , intense colors and let them mix on the paper.
Long Neck Ostrich
watercolor painting on 140 lb watercolor paper