What Makes Curly Wood Curly

A piece of curly walnut

The picture above is an exceptional piece of Claro Walnut with a ton of deep curl. I'll be using a piece of this wood to build a mountain dulcimer for a friend of ours in Texas. Since I'm using this nice wood, I thought this would be a good opportunity to talk about curl.

Most of you have seen a cross section of a log and seen the growth rings of a tree - it's just a set of circles with little ones in the middle and getting bigger as they go to the outside. When we get a plank of wood, the grain is usually just a shallow arc from a few of those circles (like below on the left). That gives you a normal grain pattern. With curly wood, those circles aren't nice and smooth - they have wobbles and dips and jags (see image below on the right). Sometimes that is caused by stress, sometimes by disease or parasites.

On the left is a simple grain pattern like most trees have - just part of a simple circle. On the right is a grain pattern of a board that will have curl.

When you cut across all those swirls, you are seeing several of those different growth rings and layers in each slice and you are seeing them at different angles - and that is what you are seeing when you see curl. In the case of this piece of walnut, there is hardly a straight line to be found (see the picture below - it is all swirls and curves).

A side view of the curly walnut

The curl will typically only be able to be seen on one face of the wood, so when I'm building an instrument, I'm careful to put that face of the wood showing on all of the visible parts. On a piece like the fretboard, this can be hard because I have three faces visible. To combat this, I cut a couple of thin slices and glue them to the sides... and now I have curl on the top and on the sides.

If you have old craftsman style furniture made out of oak, it was common to use this technique. It allows the oak "rays" to be visible on all sides of the wood.

You can see the glue up of the fingerboard to make the curl visible from all directions.