When you use water-based media, achieving results relies almost as much on the paper surface as on the quality of the colour you use. Watercolour paper must provide a suitable surface for painting according to three key factors:
The ideal amount of absorbency (or sizing) allows colour to sit on the surface of paper rather than sink into the paper itself. It also facilitates reflection of the maximum amount of light, making the colours of your artwork look more vivid.
White papers produce the brightest images, while coloured papers are used for opaque or juxtaposition techniques. When choosing the colour of your surface, consider what type of effect you are trying to achieve and how bright you would like your art to appear.
To ensure your work will stand the test of time, you will need a stable surface to work on. Long term stability comes from papers being acid-free (pH neutral). Watercolour paper is recommended to support a wide variety of techniques and to keep paper and art intact for a long period of time.
Once you have settled on your surface of choice, remember that you can prepare your paper prior to painting by stretching it. This is an important exercise which can provide you with a perfectly flat surface, regardless of how much water you use on the paper. It will also prevent cockling, or the formation of wrinkles and ridges that are difficult to remove once water has touched the surface.
To get your surface to perform to the best of its ability, read our guide to stretching watercolour paper.