Watercolour paper is a paper type that has been specifically made to suit watercolour paint but can also be used for gouache, acrylic, printing inks, pencil, pastel and pen. There are three surface types and each of these has been treated with size – a type of glue – to make it strong enough to withstand water washes and to affect the absorption of the paper which determines whether the watercolour sinks or pools on the surface.
How is watercolour paper made? Some watercolour papers are still hand-made in frames – hand dipped in a cotton pulp, size and water solution, laid onto felt blankets and then hung up to dry. Cylinder Mold Machines, that replicate this process for industrial scale production, were introduced in the 1800s and many of the respected paper makers today are proud to still be using their antique Fourdrinier-style paper making machines.
What is watercolour paper made of? The best watercolour papers have a cotton content of 50-100% cotton. They are ‘internally sized’ at the pulp stage to give the paper strength and then surface-sized with gelatine to add to the strength and achieve the correct absorbency. Although optical brighteners may be used, bleaches and acids are not used as these will adversely affect the paper over time. Therefore, the natural colour of watercolour paper is a creamy off-white. Student papers are more likely to contain chemical pulp, have bleaches added and be just internally sized.
What types of watercolour paper are there? There are three surfaces of watercolour paper - rough, Cold Pressed and Hot Pressed. The Rough surface is the natural state of the paper with a noticeable texture. Hot Pressed has, basically, been ironed to achieve a very smooth surface. The Cold Pressed is the stage in the middle where the rough texture has been given a light pressing to dull down some of the undulations but not so that the texture has been completely removed. Cold Pressed is also known as NOT as in ‘not hot-pressed’. For information on when to use each surface, see our introduction to watercolour papers.
What is Stretching? It is very highly recommended that you stretch watercolour paper prior to use to retain a beautifully flat surface. See our page on how to stretch watercolour paper for further details. The only times you would not need to stretch watercolour paper is when you are using your paper for preparatory watercolour sketches where it is not a problem if the paper cockles, you are using a particularly heavyweight paper, the paper is held in a block or you are using dry media such as pencil or pen.