The importance of stretching watercolour paper

 By Winsor and Newton

If you intend using a lot of water in your water colour painting, then it is 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 when substantial amounts of water are used. If you are working on heavyweight paper and do not intend using large washes or you are using gouache or acrylic then you do not have to stretch the paper, however 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 water colour 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 and 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 for 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 is 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 avoid creasing it. A heavy paper [300lb/640gsm] must soak for 15-20 mins, a lightweight [90lb/190gsm] one needs only 4-5 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. Then remove the paper and allow the excess water to drip off before laying the paper 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.

What happens if the paper has failed to stretch

If the paper fails it can simply be re-used by cutting it off the board, re-soaking and re-stretching. There are four faults that are the most common reasons for failure when stretching paper:

1. 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. 
2. As it is sometimes difficult to find, gummed paper tape is replaced with masking tape or brown sticky tape. These don’t stick and they don’t stretch with the paper. 
3. Too wet a sponge is used to moisten the gum strip and the gum is wiped off, preventing it from sticking. 
4. Boards or frames are stood upright to dry. The water runs to the bottom and pulls the paper away from the top. This is why paper stretching is difficult on studio walls.