Primitive Archer

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.

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

Lately I have been attempting to make double barrel  Turkish style arrows to do some flight shooting with some of my fastest bows through a chrony. I made 5 arrows, and non of them flew perfectly, but with a 36lb fire hardened hickory bow with a 285 gr arrow my  grandson shot one special arrow that flew the straightest  200 yards, or more. I need a new battery for my rangefinder. That was special. This is the first attempt at flight shooting with my own bow,and arrows, or any bow. To make an excellent bow from wood is one thing, but making a perfect shooting  Turkish flight arrow is something else. It was a fun day, and I will keep honing my skills to try , and make a more perfect flight arrow.

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.

Photos of Ash quiver.

I gave someone here an almost identical quiver to the umbrella sedge one over a decade ago, It may have been seen on PA before.