Hi Brenda. Copper is fairly easy to anneal, if you bring enough heat
to it. If you’re using the small torch tips that jeweller’s use then
you just don’t have enough heat. If you can get a #4 or better
oxy-actelene tip would work, or use a propane torch head and MAP gas.
I like using a piece of plate steel (1/4" or thicker) on top of fire
brick to rest my piece of copper on. I find the steel holds the heat
and reflects it back into the copper, which for me allows better
control over the heat build up. With the size of copper you have to
fully anneal will take a bit of patience. The idea is to try and warm
up the whole piece at the same rate, do this by slowly moving the
flame around. The copper will go through colour changes, greens,
blues and black, you want to reach the point where the copper is
beginning to glow red. Because of the thickness you would want the
whole piece at that temperature for at least a couple of minutes. If
it glows redder, no problem, just don’t let it get past orange hot.
When you have heated it long enough, remove from heat and the steel,
you can water quench, quench in pickle (don’t breath the fumes) or
air quench. All work except by quenching in pickle saves a step and I
find cleans the metal quicker.
That’s what I would do if I only had a torch available, I would
prefer using a forge. You could build a temporary one by stacking
firebricks in an oven shape and using a tiger torch for your heat
source. Either way hope it works out for you, let me know how it
Chris and Kate