Any tips for identifying reaction wood? (hardwoods)

[Tetsuaiga]

I picked up some wood recently but never got to see the tree which it was cut from.

I want to sort out any wood that could be from limbs which would contain reaction wood.

As far as I know the things I can go by are size, off centre pith or an elliptical rather than regular round shape. I've done this and sorted the wood into piles accordingly.

Is there anything else I could do, I read you can slice the log and look at it at a low angle to identify shinyness? Would applying stain to end grain also reveal reaction wood?




Thanks

 

[MusicMan]

Staining will not show anything. I don't know the 'shinyness' test but I doubt it very much.

You are correct that off-centre pith and elliptical growth rings are good indicators. Size is only of use if it determines that the log was a branch not a main trunk, as branches always contain reaction wood. It is how the tree holds the branch up.

It is possible to take a longitudinal slice through the log (as if you were cutting a plank), and machine it into fingers. If the fingers do not stay parallel that indicates reaction wood.

It is more of a problem in softwoods (gymnosperms), really. In these, the reaction wood is in tension, on the upper side, identified by wider growth ring separation. In hardwoods with one common exception, reaction wood is in compression, on the lower side, and this seems to give lower stresses. The one exception is boxwood, which despite being a hardwood (angiosperm) does have tensile reaction wood. This is well known to woodwind instrument makers, who try to select a main trunk of a tree that has grown vertical to within one degree! It is in wood turning precise items in boxwood that you get the greatest problems, since the wood will move around as humidity and temperature changes. Leaving an instrument on the lathe to finish the next day can be fatal!

For general furniture making, remember that reaction wood is on the perimeter of the wood, the stresses act along the trunk and are only on one side of the trunk. You can minimise its effect by quarter-sawing the planks.

The problem with reaction wood is that its longitudinal shrinkage is 10 - 100x the normal amount (which is very small in most woods) hence it can cause both pinching of saws (why we use riving knives) and significant distortion of planks.

Keith