On Saturday, March 24, 2012 10:30:19 AM UTC, NT wrote:
On Mar 24, 8:27*am, "Alt Beer" wrote:
The glass in an external wooden window frame is cracked and needs replacing.
The putty at the bottom of the frame is cracking and easy to remove but the putty
at the top and sides is rock solid. *What is the best way to remove hard set putty
without damaging the wooden frame?

Thanks

Heat softens it some.

+1 on that - I found I could soften the putty and remove it neatly using a scraper and blowlamp or hot air gun.
Two caveats, though - if this isn't the only pane of glass in the window you need to be really careful when using heat, as you can end up cracking another pane, and you also need to be careful, especially with anything with a flame, if there's a chance there's some rot in the frame; dried out rotten wood catches really easily.
If you're doing other work and this is a sash window it can be a lot easier to repair and reglaze it you take the sash out.