When painting trees realistically, you need to pay attention to the bark. Saplings, adult birch trees and beech trees have smooth surfaces, while the outer bark on most other trees, such as maple or oak, cracks and dries as the tree grows leaving behind a grooved, rough surface. Some of the trees you're painting may have smooth or rough bark and some may have bark falling away from the tree. The change between textures on a tree will make an interesting study within the completed work.
Set up your easel and canvas in an area such as a park with a good view of a tree as your subject. Draw a charcoal or pencil sketch before beginning. If you can't work outside, use a photograph as your model.
Fill in the darker areas of the tree trunk with cool greys darkened with ultramarine blue.This will create a strong, almost black hue. Use a bristle brush for applying these areas to cover the area faster.
Blend the cool grey with just a touch of ultramarine blue and use it to fill in the areas of medium shades on the tree trunk.
Blend the medium tone with a touch of white paint to create the light tone and use a bristle brush to apply it to the tree trunk in the areas where sunlight hits it.
Use the sable brush to blend the patches of light, dark and medium lightly onto the trunk of the tree creating a patchwork of colour tones. This will be the basis creating the appearance of older, dry bark on the canvas.
Mix the cool grey and blue with a touch of purple to create a darker hue to draw in the wrinkles on the lighter and medium tones of the trunk. Draw the lines with the side of the brush for larger areas and with the tip of the brush for finer cracks in the bark. If there are areas where the outer bark separates from the inner bark, apply a small amount of paint outside the edge of the bark and blend it smoothly into the paint already applied on the trunk. Pay attention to the way in which the outer bark casts a shadow on the inner bark.
Study the way in which the sunlight reflects off the bark and the irregular places it appears. Add a cadmium yellow light to the white paint and using a thin sable brush apply it to the bark where sunlight strikes the tree. Don't blend these lines. The yellow will contrast with the purple in the dark colour you blended, giving greater depth to your painting.
Use white paint from the tube and a fine brush to add a few more strokes of light to some to the bark to add even more dimension.
Always use clean brushes, and if you don't have one to use for each colour, clean them in between use. If you are simply adding one more colour to a blended hue, you may use the same brush after wiping off the excess. The same method and palette can be used for painting with acrylic paints.