Most of the online advice I found focused on re-using the sash. I don't have any use for the old sash. I'm after the old wavy glass for another project. They are divided lights, 3 long rectangular lights per sash, 2 sash, probably 36 linear feet of putty to remove.
Options found were steam or heatgun, and a chisel.
Here is one suggesting brushing on 50/50 bleach/linseed: http://homeguides.sfgate.com/dissolve-window-putty-98740.html
Another post reported on brushing with kerosene.
Does not needing to respect the wood open up other options?
1) I suppose I could waste a router bit to get the bulk out, but if I hit a point with legs (in contrast with flat triangles or diamonds), I'm guessing it would crack the light. Big down side is the all the dust, likely lead toxic
2) I could cut up some plywood, screw it together as a steam box. That'd be quick, but when it comes to putty, heat is heat, no? Historic Preservation: https://www.youtube.com/watch?v=XVoc9HnHtCA Dave Bowers: https://www.youtube.com/watch?v=I1bjOENLTQA
3) Or just soak the entire sash in water for a couple days.
4) I own a general heat gun.
5) I suppose I could power up the table saw to rip the rails and stiles to within an 1/8" of the glass, maybe the mullions as well. This would eliminate the support given to the lights by the sash and require removing the putty from the glass without that support.
6) lots of varying advice: http://www.diychatroom.com/f4/removing-putty-old-windows-glass-replacement-30292/
The one thing I have going is that I need only two intact lights for the current project, but would really like to preserve all five (one is cracked).
So I guess there are two tasks, remove putty from the lights, and remove the lights from the sash.