At a Landscape in Pastel class I taught at the Michigan Art Center, we spent some time reviewing the variety of tree trunk textures and how best to convey their sometimes complicated patterns of knots, crevices and bald spots.
Below is a simple, quickly-done pastel painting of a tree branch (the reference photo is below). Along the Huron River at Gallup Park in Ann Arbor, MI., you can often find old twisted trees climbing up from the river bank and hanging over the water (such as the tree below).
To convey the texture of the branch, I followed this approach:
A simple sketch of the darkest green (almost black) for the underside edges and other shaded areas.
Application of a variety of mid-value hues, including (as can be seen) browns, blues, yellow ochre, gray, and a very light blue-gray. The trick is to apply the various hues is short strokes basically following the direction of the growth. Since this branch has a twisted character as it reaches over the water, the darker values stretch along the wood to help convey the sense of reach.
The highlights (white-ish areas) reflect the sunlight and are done in very light blue (not white).
Here is the reference photo of the tree on the Huron River (a portion of the lower branch hanging over the river is the subject of the pastel):
The texture was built by applying these different strips of color and varying the direction of the stroke.
Trees and branches make excellent subjects for your sketchbook. Make sure you learn about those trees: know how they grow, sway in the wind, age, etc. That way, your painting will be more realistic, and you will have more fun creating their unique personalities on canvas.
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