The idea of stretching watercolor paper was one that I found strange. My first thought was “how and why would do I do that?“
After looking into it, I discovered that this process doesn’t actually stretch the paper. Instead, it involves thoroughly soaking the watercolor paper so that the fibers “plump” and the paper size expands slightly. Then, while it’s still wet, you staple it down to a board, and as it dries, it contracts slightly against the staples, and this flattens and smooths it.
In addition, soaking the paper also removes some of the sizing. Sizing is a wash that the paper manufacturers apply to paper to change the way it absorbs paint or ink. Sizing is usually is made of some sort of gelatin, which if applied in excess, can impede the absorption of paint more than desired. Therefore, some artists like to remove some of the sizing via the stretching process. Now the caveat here is that you don’t want to remove all of the sizing, so you must limit how much time you soak the paper. In listening to other artists, 10 minutes seems to be the upper time limit for soaking the paper.
Here's how to stretch watercolor paper. (Not that you'll need a piece of gatorboard a little larger than the paper you want to stretch, a regular household stapler and a water source.)
These steps are from a great video about stretching watercolor paper made by Colorado artist Lorraine
Watry. She first shows how she transfers her drawing to the paper and then starts the stretching process at 14:37.
The purpose of stretching watercolor paper is to keep the paper from buckling when you paint on it. If you ever added a bunch of water to a loose sheet of watercolor paper, you’ve seen how it buckles. This is because the fibers where you are painting get wet and expand while the rest of the paper stays dry. Stapling or taping the paper edges down securely before you start painting stops this from happening.
Keeping the paper flat is important because if your paper buckles while you are painting, you can get paint color running into areas that you didn’t intend. In addition, once it dries like that, you won't be able to frame the painting. Hence, it’s best to tack it down before you start to paint.
Stretching watercolor paper is useful for larger paper sizes, such as 11” x 15" or more. Smaller paper
sheets can be taped down as they are, without going through a stretching process. Some artists will tape and staple dry watercolor
sheets down to the backing board to minimize buckling.
I recently learned how stretching watercolor paper can go wrong when you try to go the cheap route. I bought a full sheet of Arches watercolor paper and used Lorraine Watry’s technique to stretch it onto a board. She recommends using gatorboard, but when I went to buy gatorboard, I found that it was quite expensive. So I went to my local art store, and found some board that had a foam core with a hard outer shell just as she described. I thought it was the same thing as gatorboard. Nope.
The picture below shows the result. The paper is
perfectly flat and the staples held, but the board bowed. That will be awkward to paint on, but that's my lesson learned. Next time, I’ll shell
out the extra money to buy REAL gatorboard, which is much stiffer than this cheap foamcore board.
Or maybe I'll just avoid the whole soaking/stretching process all together. After watching this great video by Steve Mitchell over at the Mind of Watercolor, I'm thinking there are better ways to prevent paper buckling.
I'll be looking into buying a commercial stretcher, some 300 lb paper and some watercolor board, since I agree, stretching watercolor paper is a pain, and gatorboard is expensive.
If you have completed, dry paintings that are buckled and warped, you can fix them with these steps:
Here's a short video for a visual demonstration of these steps: