I apologize Fancypants, I wasn't questioning whether it was or not, just stating that I had never heard of a specific knife for said and thus would have never guessed that was what it might have been.
Nor would I have made the correct guess if you posted a picture of a "lead window soldering iron/gun". The thought would never have crossed my mind as a consideration.
There is an old Church here in Town, in disrepair, that has several hundred sq ft of leaded windows in it. The Lions Club, which I was President of for 4 years, owned if for 40+ years and it has been sold 2 or 3 times since then. To wit, I sent the wife down to take a picture for to see: