If you intend to use a lot of water in your watercolour painting, then it’s important to stretch your paper before starting to avoid cockling. This is where the sheet wrinkles and forms ridges that are almost impossible to remove. If you are working on heavyweight paper and do not intend to use large washes, or you are using gouache or acrylic, then you do not have to stretch the paper. But the benefit of stretching your paper is the freedom to use as much water as you want, when you want.
There are two ways to stretch watercolour paper:
Stretching on a flat board
Board: This is the most common way of stretching paper and spruce drawing boards (draughtsmen’s boards) are the best because they are hard wearing and durable. However, they are not easy to find. MDF board can also be used but it should be sealed beforehand so that water doesn’t penetrate. For paper under 24″ square a 12mm board thickness is suitable; for larger sheets, increase the thickness of the board to prevent warping. A thicker board is best because you can use both sides. Alternatively, you can brace the 12mm board on a frame.
Paper: Acid-free paper is the best paper to use if you want your work to last a long time. This is because acidity embrittles the paper and eventually makes it too weak to handle.
Whatever paper you choose, use the heaviest sheet you can afford, for the simple reason that it will be more robust and less likely to be bent in long term storage. Paper can be stretched up to a size of approximately 1.5m x 2.5m but if you go beyond that, the tension in the paper will be too strong.
Procedure: Allow 1″ for gummed paper tape all the way round your paper when cutting to size. Fill a large sink or bath with water and submerge the paper, rolling or folding it as necessary, but avoiding creasing it. A heavy paper (300lb/640gsm) must soak for 15-20 minutes, while a lightweight one (90lb/190gsm) needs only four to five minutes.
If the paper is too large to submerge it can be soaked on the board but allow up to 25 minutes soaking on each side to ensure expansion of the paper.
After soaking, remove the paper and allow the excess water to drip off before lying it on the clean board. Using traditional gummed paper strip, tape down the edges and leave the board to dry flat. Both sides of the board can be used – simply stand the board on four ink bottles to let the air circulate.
Stretching on a purpose-made frame
It is also possible to purchase stretching boards or “paper stretchers” from your local art store.
What happens if the paper has failed to stretch
If the paper fails to stretch you can reuse it by cutting it off the board and going through the soaking and stretching process again. There are four faults that are the most common reasons for failure when stretching paper:
- The paper has not soaked long enough. It looks flat when dry but still cockles when painted on. Running paper under the tap will not be sufficient to soak it.
- Gummed paper tape, which is sometimes difficult to find, has been replaced with masking tape or brown sticky tape. These don’t stick and they don’t stretch with the paper.
- Too wet a sponge has been used to moisten the gum strip and the gum is wiped off, preventing it from sticking.
- Boards or frames have been stood upright to dry, making the water run to the bottom, pulling the paper away from the top. This is why paper stretching is difficult on studio walls.