The last process mentioned from Parker's Factory Process doesn't mention boiling so might be browning but you would need to be a chemist to figure it out.
Not a chemist, but I do note it included a pass in the "Steam Room". Exposure to steam will convert the rust to black same as boiling. One thing one has to be careful about in interprting old writing on the subjest is the process itself was quite often referred to as "Browning" regardless as to whether it was done to produce a black or brown finish.
