Fire Hardening

[Burnsie]

I just watched a video of Clay Hayes making an awesome fire hardened hickory bow.  Got me wondering - as good as Osage is for a bow wood, would there be any added benefit to give it a fire hardening treatment? 

[Hamish]

I've never heard of anyone trying it with osage. Osage is denser already. It is also more susceptible to getting drying cracks than whitewoods. Osage also doesn't like to be bending at extremely low moisture content, as it becomes brittle in tension.

I don't know the scientific reason that makes the heat treatment improve whitewoods. I'm guessing it could be something like the air still in the wood cells, and vessels is heated out, the empty spaces shrink, and compress the wood, leaving more lignum for the same dimensions??? Or it could be some other sort of chemical reaction?

Denser wood species, possibly don't have as much air trapped in the cells and vessels, so there is less opportunity to compress, and therefore not as much change for  improvement to occur.

Pure speculation on my part. Hopefully someone with the correct knowledge will chime in soon.

[Del the cat]

Heat treating the belly can certainly increase the performance of Osage.
But I don't know about "fire hardening" vs heat treating.
Del

[Eric Krewson]

I heat treat all of my osage bows but never tried to fire harden one.

[Burnsie]

I heat treat all of my osage bows but never tried to fire harden one.

Eric - is your heat treating to make corrections or add deflex, recurves...etc. - or just done to the full length of the bow after it has been tillered and basically finished?

[Chumash]

Hardening wood with fire to make it more durable is a very old technique. It was used to harden the ends of grave sticks and the tips of the first spears.
Heat changes the cell structure (caramelization, carbonization) and reduces the equilibrium moisture content.
The wood becomes harder and more durable (less susceptible to microorganisms and fungi).
For example, so-called thermo spruce used as exterior cladding for houses lasts just as long as larch wood.
Heat treatment—whether with a heat gun or over an open fire—has a lot of potential for bow wood.
But be careful, because although the wood becomes harder and more durable, it also becomes more brittle. Too much heat or heat for too long is not good for any wood.

[bassman211]

The times that I used heat with a heat gun on Osage... to get the wood  straight on a form lining up the tips with the handle, and belly heating with a heat gun to help hold its shape. You can fire harden elm,hickory, and even white oak, and some other woods with good results, but Osage being the bow wood that it is , and being hard to get your hands on a good stave really doesn't need to be fire hardened.JMO

[Chumash]

In my opinion, fire hardening and heat treating are the same thing, just the intensity is different.

When wood is formed by using dry heat, the same thing happens in the cells as if the wood is just exposed to heat...

[Eric Krewson]

Full length toasting but not like putting the bow over a fire pit, I refine the tiller after toasting.

I darkened out the lighter spots after I took the picture, after the final tiller some of the darker areas only showed a hint of toasting.

I had so much osage back when I was making bows (still do, I live in osage country) that I didn't worry abut ruining a stave which I never did by toasting a sluggish bow.

[Pat B]

I've used heat and a caul to remove bends, twists and humps from osage then the last step is to go over both limbs and heat until the color changes like Eric does. That is basically to set the changes. I let it rest over night at least to cool completely then let it rest a few more days to rehydrate before removing it from the caul.