I have the problem with some old double hung sash windows.
I tried the heat gun method with some success but still managed
to crack a few panes not from excessive heat but from pressure
applied scraping the putty out. I found that the glass was not
necessarily evenly supported by the rebate on the other side.
I've switched to using a multi tool with oscillating saw blades.
With a little care this is a little easier and quicker, but patience
is the key word whatever the method.


use a heat gun, (essentially a hi-temp hair dryer)
or --very-- carefully with a propane torch. either one
will get the glass hot enough to crack it, so be careful.
also, try not to breathe the vapors.
be patient, and let the heat source do the work.


Be aware, too, there are probably glaziers' points (little metal fasteners) under
the putty, that may have to be pried out of the wood.


Also, old window caulk can contain asbestos
http://www.greenstreamenvironmental....-your-windows/
John T.


My understanding is that asbestos is relatively safe to work with
in a non-friable (not a dust) state. Particulate masks are always a good idea,
as the paint may be lead based as well...


Badly deteriorated putty or caulk is friable - when you start to
mess with it. especially using the multi-tool
Also - a responsible worker will not only protect himself with
properly rated respirator - but do his utmost to prevent the
microscopic fibres from dispersing into the room and vents & such.
John T.