Studying the crotch

Every now and then I’ll use the word ‘crotch‘ when talking about wood and I have been ordered by the Good Lady Smithery to explain what the hell I’m going on about.

It’s pretty simple – look at that tree over there. No, not that one… the other one. The one with the pigeon in it and the knobbly bit that looks like a bum.

sweet chestnut crotch
There’s a bowl in this sweet chestnut crotch somewhere

See where the branches divert away from the trunk and head off to do their own thing? See the Y-shape they create as they leave the trunk? That’s the crotch, that is. And if you can’t work out how it came to be called that then you should have paid more attention in your school biology lessons.

The good thing about crotch wood is that rather than just having regular grain patterns that you might see in, say, a normal branch, this features a collision between two or more lots of grain running in different directions, thereby creating more visual interest and perhaps contrasting colours and patterns. And if the crotch features more than one branch, then the more interesting and complex it becomes. This is more noticeable in hardwoods which already feature striking grain, such as oak or walnut, but isn’t so obvious in more bland woods like sycamore.

Cutting a lump of spalted silver birch crotch into bowl blanks. The pith is particularly susceptible to checking so has to be removed (that’s the bit on the ground)

Crotch wood comes with its own unique set of issues, however. A regular lump of trunk, when fresh, will begin to shrink as it dries out. This can be seen by cracking (aka ‘checking’) which starts at the centre of the rings (aka the ‘pith’) – which isn’t necessarily the centre of the round log – and goes to the outside surface where the bark is/was.  But grain that heads all over the place inside the crotch is less predictable. Checking still happens, but with two or more piths involved the cracks can go in different directions and create warping which either ruins or improves the whole piece, depending on your point of view.

So there you go. Now you know. Crotch wood isn’t as rude as my wife – with her mind in the gutter – seems to think it is.