Look for a puty chaser for an electric drill.

It cuts away most of the putty leaving a very thin portion that is easier to then chip out.

Don't feel bad about it - it happens! Someone had used what I think was mortar on my super skinny, badly abused muntins. Even after the glass was broken &/or removed, heat wouldn't budge the 'putty'.

Heat and glass are a bad combination.

Here are tool suggestions from someone who restores windows for a living....

Any of jade's posts on that forum are well worth reading.

Here is a link that might be useful: window tools

A HEAT GUN?! Don't come near old glass with one of those!

As stated above, there is a drill attachment to use for removing putty, though I don't have one. My usual tool is a narrow putty knife, and I remove points with a screwdriver by rocking them a bit--I have yet to break any glass.

At work we have a steamer for softening glazing, but I have never used it.
It depends on if you are any good with a heat gun; it requires a delicate touch. I got all of the glass out of this door with a combination of heat gun, chisels, scrapers. The putty was the hardest stuff I have ever come across, very cement-like. Didn't break any panes or tiles, which is good because much of it is irreplaceable. Under the best circumstances, count on breaking 10% or more, either on the way out or when re-installing it. There can be unseen flaws in the panes that will take advantage of the handling so become cracks, and those aren't preventable.

You must keep the heat turned down, you must keep the air pointed sideways at the putty, not the glass, and some people have success using a "dodge", a sheet of thin flameproof material, that is laid against the glass and takes the heat in its stead. It will not permit turning up the heat, but it's a bit more insurance if extremely unhandy. I don't use a dodge.

Casey

What a great door Casey! My aunt has a similar one, but not as ornate; hers has glass like on your two sides, but it goes around all four sides of the center pane...no other fancy stuff like your above portion. I think her house dates from the 1880-90s...but had been extensively redone inside, alas.

Yep, it's some door. I was told it was from an 1884 house. And that seems about right. The sharp primary colors of the glass are amazing; most colored windows from that period had mauves, light greens and other shades I don't really care for, so I lucked out. And it was the _exact_ size I needed for my kitchen door, 34"x83". I had only to plane a tiny amount off of one edge.
Casey

The pros are using steam to deglaze sash these days, apparently.

Graywings, as you restore your windows there is no better resource than John Leeke's Historic Homeworks window restoration forums, with his (free) online videos and hundreds of interesting discussions by experienced pros:

Here is a link that might be useful: Sash deglazing thread (steam, heat gun and other methods)