On 14/04/2021 10:12, GB wrote:
Removing old very hard putty - what's the best way to do this? It's in a
Critall steel window, and I wouldn't be surprised if it's the original
1930s putty.

I've been using an old wood chisel and a hammer, but it's very very slow
work.Â* Is there a much better way? Not keen on a blow torch, as there's
probably loads of lead paint on it, but would a hot air gun help soften it?

.
Correct, warming it up will make a surprising difference. Especially
easy with Critall windows because you can supply heat to the frames ane
warm it up from the inside. Do it gently until you find the right
setting to avoid risk of glass cracking (unless the glass is already
cracked, of course).