Watercolour paper is finicky. It is either too soft, too thin, too smooth, too rough, can have insufficient sizing ...
Paper for painting is sold by its weight in pounds (lbs) or grams, in sheets or blocks or pads, its surface texture, and its content.
In the picture at the top, I used 300 gsm sketchbook. This paper absorbed less of the water and so the pigment was more diluted, drying paler, and could be glazed for deeper colour. There is no cockling.
In the other (110 gsm) sketchbook, the cockling is very evident. The paper absorbed more water, making it buckle, and glazing would not be satisfactory.
Cockling on 110 gsm watercolour paper
In metric terms, the weight of 500 sheets of paper can be:
- 90 grams per square metre (gsm) — great for sketches, notan thumbnails, but too thin for watercolour. Imperial equivalent is 60 lbs.
- 110 gsm/74 lbs — often on a school requirements list, but not recommended by most serious artists for paintings. Again, great for sketchbooks.
The two most popular papers for watercolour painting are:
- 300 gsm/140 lbs is the paper of choice for many artists, although it may need stretching to prevent cockling, especially if you are using very wet washes.
- 640 gsm/300 lbs is excellent for painting your 'masterpieces'. Although the cost is greater, the results are far and away worth paying the extra.