Wood knots are distinct, circular or oval imperfections visible in timber. These natural features represent areas where branches once connected to the tree’s main trunk. Their formation explains the unique characteristics they impart to wood.
The Biological Beginning of Knots
Knots originate from the growth of branches on a tree. As a tree increases in height and its trunk expands in diameter, the main stem progressively envelops the bases of these developing branches. This process integrates branch wood into the trunk, forming a knot.
The nature of a knot depends on the condition of the branch during its incorporation into the trunk. A “live” knot forms when the branch is still biologically active and growing with the tree. The wood fibers of a live branch remain intergrown with the trunk, resulting in a dense, solid, and firmly integrated knot. Conversely, a “dead” knot occurs when the trunk grows around a dead or detached branch stub. This leads to a less integrated knot that may become loose or fall out during processing.
How Knots Appear in Timber
In lumber, knots appear as visually distinct areas. They typically appear as darker, circular or oval shapes against the lighter background of the surrounding wood. This color difference often arises from variations in wood density and the presence of extractives within the knot.
A defining visual aspect of knots is the disrupted grain pattern around them. Trunk fibers grow around the embedded branch, creating a swirling or irregular grain that deviates from the surrounding wood’s straight pattern. Tight or sound knots appear solid and are fully intergrown, whereas loose or unsound knots may show cracks, decay, or even be missing, leaving a hole.
Knots and Wood Characteristics
Knots influence various characteristics of wood, impacting both its practical applications and aesthetic appeal. Structurally, knots can reduce wood strength and stability by disrupting the continuous flow of wood grain. The extent of this reduction depends on the knot’s size, location, and condition within the lumber.
From an aesthetic standpoint, knots can be viewed in different ways. While some consider them defects, others value them as natural features adding character, especially in rustic wood products. Working with wood containing knots can also present challenges. Their dense nature and irregular grain can make tasks like planing, drilling, or finishing more difficult, potentially leading to tear-out or tool dulling.