Explanation of patterns (figuring) in wood.
Woodturning is one area of woodwork that actually prefers strange pieces of wood - pieces that have knobbly growths, bulges, wavey grain, and even fungus infection. As long as the wood is still in good physical condition, it makes excellent material for making turned items. Bowls in particular benefit from figuring, as they have a large surface area to show off the wood.
Wavey grain
This can occur for a number of reasons, but the most common cause is from stresses built
up in the tree as it was growing. If a branch was twisted strongly, the grain will not be
straight. Parts of the tree where 'joins' appear, like branches, forks, and roots have
wild grain patterns, often called 'flame' figuring, because the grain cannot smoothly
merge between the two limbs. The location of flame grain in a 'crotch' piece of wood (a
fork) is shown in the diagram.
Bulges, bumps and burrs
Smooth bulges on a tree are usually were the surface has repaired itself, following the
removal of a branch. This would contain slightly wavey grain. The other possibility is
that a bulge is a 'burr' - an abnormal growth on a tree.
These can
be speckled or smooth and can vary in size from tiny bumps to 20 inches or more in
diameter. Speckled burrs are generally the best (see photo). The interior of these
growths consists of hundreds of tiny buds that have failled to grow properly and have
continued to be produced, like cancer, to form a tumour.
Smooth burrs merely consist of wavey grain, but it differs from other wavey grain in that
the grain can form rough circles round the interior of the burr. This is very impressive
on a bowl. It is also possible to make turned items with part speckled and part smooth
burr (see photo) so that the design is not overwhelmed with detail.
The most common woods to have burrs (in the UK) are elm, oak, and walnut. I use elm for almost all of my turning (see Woods that I use ) and I often get little patches of speckled burr, which add character to the wooden item.
Spalting
When a dead piece of wood has been lying on the ground for about a year or more, fungus
starts to invade. If you collect the wood quick enough, and dry it out, the fungus will
be killed and the wood should still be in good condition. However, you may find very
clear thin black lines in a winding pattern across the wood. This is the result of the
fungus and there may also be discoloured patches of wood on one side of the line.
Beech is the usual wood to find spalting in, but it also occurs in elm, although usually at the same time as the wood begins to soften and rot.