Is that to say his statement is correct that bone charcoal color case hardening is "inappropriate" as he indicates?
From everything I have ever seen or read the bone charcoal method has well over 100 years of use, performance, acceptance and still is the preference today and the method still used on the better and best guns.
If he were simply to say that this is one alternative method to BC, and also indicate that originally the firearm had BC color hardening, that would be a different situation.
If the bone charcoal method is not done correctly, he is right it will warp the parts.
The chemical and heat process is and old deal using cold blue from Brownells and a propane torch.
Did he mention that it wears off if you look at it to hard?