I would have to agree with Keith about the possible use of fire.
There was a world class knapper who was born during the 19th century, who could probably outknap any modern knapper alive. When he was asked about using fire, with regard to the "fire and water" knapping method (which was a common belief during the 19th century) he would never answer people. The reason why is because he did use fire. But, he did not use fire in the fire and water knapping method. He used fire on pieces on antler, if he wanted to create a heavily rippled flake scar style, as seen in some old points.
In communicating about this with the late Philip Churchill, Philip offered the opinion that by briefly holding the tip of the antler over a flame, the heat caused the moisture to evaporate. And, this would have rendered the tip harder than a moist tip. Naturally, a harder flaker tip would lead to more rippled flake scar patterns.
Anyway, this knapper would never affirm that he used fire. Most likely, he did not want other people to know how he was making his points. Obviously, the money would be gone if everyone followed in his footsteps. But, he did finally admit that he did use fire, only not in the manner that people may have suspected.
Since learning this, I have "heat treated" my antler flakers, from time to time, over an open flame. I do this if they become damp. From what I can tell, it seems that a brief firing does quickly make the antler harder.
Also, everyone should thank the moderators that this information can even be posted. I was told by other moderators on other forums that no one is interested in how Native Americans carried out their flintknapping practices. Even the Native American methods that can potentially produce late stage outrepasse, are not being discussed, much less looked at. Everyone should be thankful that this is one of the few places where the discussion of evidence-based flintknapping is actually allowable.