DEMOS & TIPS
Paper Weights - Buckling - Stretching Paper
By David Cuin
Papers for watercolor are not designated by thickness, which would be difficult to measure on a textured surface, but more usually by weight. The weight of watercolor paper is based on a ream (500 sheets) of "full" sheets. A full watercolor sheet measures 30" x 22". The weights in which we are most interested are 140 lb and 300 lb. The 140 lb paper feels like thick paper or thin card while 300 lb paper is much stiffer, like cardboard. Three textures are available in these weights - hot-pressed (smooth), cold-pressed, sometimes called "Not" meaning not hot-pressed (lightly textured), and rough. A 90 lb weight paper is also available but not recommended due to its tendency to buckle badly when wet. One manufacturer (Saunders Waterford) produces a 200 lb weight paper that is only available in cold-pressed and hot-pressed at this time.
Which weight of paper you choose to paint on depends on the size of painting you want to make, the technique you want to use and your income. The big determining factor is buckling, or "cockling" as it is sometimes called. When paper gets wet it expands and buckles, the bigger the piece the more severe the buckling. You can offset this by using thicker, i.e., heavier, paper. If you can afford 300 lb paper, you can paint up to half sheet size and, depending on how much water is in your painting technique, perhaps even full sheet without worrying too much about buckling. But, 300 lb paper is expensive; you may need to use 140 lb paper, which is what most artists do. If you secure the edges of the 140 lb paper well, it can be used up to quarter sheet size (15" x 11") quite successfully. Larger works, or those using techniques that employ a lot of water, require 140 lb paper to be pre-stretched to reduce its tendency to buckle.
When dry paper fibers become moist they expand. Typically in a painting, a wetted area may be adjacent to or surrounded by dry paper. The expanded dimension of the moistened fibers has nowhere to go in the plane of the paper, and it can only be accommodated by rippling up and down out of the flat plane. You can easily test this for yourself by taking some ordinary typing paper and wetting a patch; the ripples rapidly appear. You can minimize the tendency to buckle by pre-stretching watercolor paper.
There are several ways to stretch watercolor paper but in principle the paper is wetted, securely fastened down at the edges to a strong rigid board, then allowed to dry. The way that has worked best for me is to use a sheet of plywood or Homosote (see below) not less than 1/2" thick and at least an inch larger in size than the paper to be stretched. Cover the plywood with a waterproof membrane to stop soluble compounds in the board from being transferred to the wet paper. I use aluminum foil but plastic wrap or a coat of house paint would also work.
Allow the paper to dry for 24 hours before removing it from the board.
© 2021 by David Cuin, all rights reserved.