Break Old Plumbers Putty Bond?

There used to be a hairdressers shampoo sink in our current mud room. I'm trying to install a utility sink there. The piping out from the wall is a mixture of cast iron and galvanized (if cast iron has shiny black paint?) I would like to remove several sections back down to where I can put in a standard trap for the sink. There is a white-ish substance in the threads at the joints. Months ago I sprayed Liquid Wrench on the joints and then went on with my life figuring that it would be easier to deal with when I had time later if I did that. The only thing that comes off easily is the cap. Sigh. I have burned up two hair dryers trying to heat the putty or whatever the white-ish stuff is. The house is 60 years old, so I'm not sure what substance this could be or how else to soften it to allow me to turn the pipe. The pipe sticks out of a wall covered in knotty pine. (or I would've been tempted to spray it with either WD-40 or Liquid Wrench and just toss a match at it.) My husband put a big pipe wrench on it and succeeded only in moving the pipe inside the wall (yikes!) Anybody got any ideas? Any legal chemicals to help with this or just brute force and patience?

you will probably have to saw it off and then chisel out
the threads inside the fitting


either that or ou could just cut it back and
leave about 2 inches out of the wall

then simply install a rubber fernco clamp on it

Probably white lead, not putty.
If you have room to get a back-up wrench on the cast fitting at the wall and try tightening. It's amazing how often that works to just get it started.
Or just cut the pipe and use a no hub band or a FERNCO fitting and go to PVC pipe.

Your solution of cutting off the pipe will certainly be quicker than the route I had taken since posting. I have been carefully brushing brush cleaner (toluene,acetone, etc) around the joint and chisling the stuff out with a steak knife, then applying the pipe wrench and beating on it with a hammer. I will run right down to the equipment rental company tomorrow and do it the way you say. By tomorrow night I should have a utility sink! Thank you again for your kind replies.