A hardwood with a straight grain. It is a hard and durable wood that carves well and holds its shape. The distinction of walnut is its rich brown color, which can vary dramatically, from very light to very dark brown. The middle of the walnut tree produces the darker wood, and the outer layer of the tree, just beneath the bark, produces the lighter brown shades. The wide color difference of quality and wood color in the trunk of the smaller, slow growing walnut tree is the reason walnut knobs are more valuable and making quality knobs is more expensive.