Shading with acrylic paint can make your artwork look more lifelike and three-dimensional. Shading is generally reserved for areas of dark or shadow in an image, so studying an inanimate object under light sources from a number of different angles can help you to see where the shadows should be placed in relation to an object in a painting. With acrylics, shadows can be created by mixing paint colours and by building layers.
Practice shading by drawing a circle on a sheet of paper with a pencil. Imagine that the circle is a three-dimensional sphere and there is a light shining onto it from the right-hand side. Shade the left-hand side of the circle using short pencil strokes. Following the curve of the circle, the pencil marks should be drawn so the short marks disperse in all directions. As your marks approach the invisible line separating the left and the right sides of the circle, ease off on the shading--apply less pressure on the pencil and allow more blank space between marks--so that the shaded area gradually becomes lighter. This will create the effect of a smooth, round surface. The left-hand side of the circle should be darkest, with the shading growing lighter toward the right-hand side of the circle. The shading should make the circle look like a sphere.
Mix a bold colour of acrylic paint, such as red or blue, with white acrylic paint. Dip a large paintbrush into the mixture and paint a single stripe of colour onto a sheet of paper. Add a small amount of the bold colour to the mixed paint and again dip your paintbrush into it and paint a second stripe to the left of the first. The stripes should touch. Continue to add more bold-coloured paint to the mix, each time dipping your brush and painting a stripe to the left of the previous stripe with the intensified pigment. Notice how this creates a shading effect across the page; the tone changes gradually from dark to light. Wash your brush thoroughly, pat it dry but maintain a little bit of wetness in the brush, and gently move it across the stripes to blend them.
Choose an inanimate object to paint, such as an apple or an ornament, and position a light source to face the object. Observe the locations of dark and light on the object. Using the practised techniques, paint the object on the canvas by building up bolder colours and tones of acrylic paint for the shaded areas. Move from lighter shades to darker shades when painting to avoid making the highlighted areas of the painting appear "muddy." With a clean and slightly wet paintbrush, blend the shades while the paint is still damp; be careful to do this before the paint thoroughly dries, as acrylic paint tends to dry quickly. Use several layers of paint to accentuate specific highlights and shadows. For these details, allow each layer of paint to dry before applying more paint.