As watercolor paints are semi-translucent, papers play an important role in the finished work of art. The paper’s brightness and texture are just as critical as the choice in pigments. Papers most suitable to this water-based medium accept a watercolor wash evenly with reproducible results.
The most important ingredient that that makes a high-quality watercolor paper is the sizing - the invisible material used in the paper-making process to make the paper more resistant to water. The sizing enables the washing out of color and reworking the same area, which is essential for watercolor papers. Substantial sizing also prevents the fibers from buckling.
There are a variety of surfaces for different watercolor applications, but for the most part watercolor papers are classified as Hot Press (HP) exhibiting a smooth surface, which is prefect for fine detailed images; Cold Press (CP) having a more textured surface; and Rough (R), as the name implies, a highly textured surface.