Watercolor pigments vary: some are transparent and some opaque, some stain the paper and others do not. Opaque pigments and pigments containing white are not suitable for glazing. Using a small piece of watercolor paper, draw a thick, black horizontal line using a permanent marker. Select the watercolor pigments that you think are opaque. Mixing the paint with a small amount of water, paint vertical swatches of color across the black line. The opaque pigments will somewhat cover the line with color, while the transparent will not.
To test which pigments stain the paper, mix the paint with water and paint a swath of color onto the watercolor paper. Once it is dry, paint back over the painted areas with clean water. Dap the paint with a cloth. The non-staining pigments will dissolve and can be removed; the staining colors cannot be removed from the papers surface. It is important to understand the nature of the pigments before using them in glazing. Staining pigments work best as the first or second layers when glazing with watercolor.
To begin glazing with watercolor paint, the watercolor paper must be wet. Using a large brush and clean water, wet the paper in long horizontal strokes. Place the paper on a water-resistant surface such as Plexiglas. While the paper absorbs the water, prepare a palette of paint. Paint in the foundational color of the composition. Allow the foundational colors to dry completely. Mix water and paint to a transparent consistence for glazing. Create new colors and build detail and value by glazing additional transparent colors over the foundational colors. Continue deepening colors by adding more glazes of transparent color.
Allow each layer to dry before glazing with more color. Watercolor paints are water-soluble so work with long strokes that flow without heavy pressure. A hair dryer can be used to hasten the drying process. All watercolor painting has an element of unpredictability that adds to the beauty of a composition. Working in transparent glazes adds a unique freshness to the finished work. The best choice in watercolor paper, when glazing, is cold press, which has a smooth, even finish.