Guest, Mike -- I'm delighted you've revived this thread, because on re-reading it I have discovered a link which is relevant to a question I asked six years later (in this thread: Questions about Hughie Graham)! The question concerned a line which goes:
And ye may gie my brother James
My sword that's bent in the middle brown

I was wondering why anyone would want "a sword that's bent"...
The link that Malcolm Douglas provided in his post, above, after discussing weapon knife vs. wee pen knife, goes on to mention:
"...please note the Hugh the Graeme error in MacColl or the Corries songbook, or both - his sword was not of the 'the metal bent', or 'the metal burnt', but of 'the metal broon' in contrast to his other sword which is of the 'metal clear' "

Not having a phenomenal memory, I did not happen to remember the factoid contained in this link all these years later, and of course -- sadly -- Malcolm was no longer around to comment... but his vast knowledge is still here to provide enlightenment -- albeit sometimes in unexpected ways...

Although this does not clarify things completely (the words bent and brown are both used in the line in question -- think I'll go revive that thread), it was a buzz for me to re-read this thread (and that link) and make a new connection...