Aluminun temp of annealing is 640-670 degrees F. Higher or lower temp may give incomplete softening. Hot working temp for aluminum varies from 300 to 925 F, depending upon alloy and procedure. Some ways to gauge temp are; tempil sticks(650F) available at welding supply, digital lazer pyrometer(cheap these days) coating surface of metal with acet.only flame and then burning off the carbon with oxy-ace flame, and the old standby, rubbing a sliver of pine wood over the surface, it should just start to char the wood,giving a slippery feel. Wax may work, try it. Don't know about the dyes.

Some alloys of aluminum don't forge/chase well. One way to tell if you have a "hard alloy(i.e. 7000 series)" is to take a small piece and see if it bends easily.......if it snaps when you bend it to 90 degrees, it might not be easy to chase and repousse. Doesn't mean you can still anneal it and try. :)
As for "how much hammer work before re annealing" ......you'll know.......the metal will seem harder..the sound and feel will tell you. FWIW, I've seen incredible repousse done on aluminum from Thailand. Looking forward to seeing what you do.
Besides the wooden stick and acet. soot......you can also use a permanent marker(Sharpie)...it burns off at the annealing temp. also.
When ever I anneal thin sheet...using the soot or marker approach......I ALWAYS also use a wooden stick(I like the sticks they give you to stir paint) to make sure that the aluminum doesn't get to hot.

While slowly heating up the sheet.....begin to rub the stick on the surface......when the aluminum is cold..the stick almost feels like an eraser ...it drags. But as the temperature rises.....rubbing the stick begins to leave a light brown mark.....and seems to "drag" less. As the temperature approaches the annealing temp. the "mark" gets darker(darker brown)and begins to slide across the surface of the aluminum. With thin sheet you need to be very careful as the "mark" gets darker.....with thin sheet I never go past "medium to dark brown mark". If you go until the mark is black......your very close to melting the aluminum.

One other "visual" effect that you get when heating aluminum......RIGHT BEFORE it melts.....the surface gets a golden hue.

Practice with a scrap first.....:) maybe even on a thicker piece if you've got one.

bill

here is a litle update on my mask project. first I made a template based on the model I made earlier.

template"

then I foldt the nose. note that this folding combined with the teplate saves time as apose to raisingh the nose.

folding nose

after that I started rough shaping by hammering on hammers fixed in the vice used as stakes. I also dit some hammering on the anvil and on wood.

rough shaping

after that I started chassing. I tried using wax but the problem is it melts like watter. almost straight to liquid. while this mide be ideal voor filling and chasing a vessel for my mask its not idieal. also with pitch I can controll the hardnes better using a hot air gun(U know the ones you use for removing paint? whats the real english word for this tool?)
downsides on pitch are that it splinter and cracks, its expensive and its harder to remove.

grts ambition.

ps: thanks for the anealing tips, I started before the replies with anealing and discored that my waterproof design lines indeed disapeard at the same time my wooden stik started to slide. just a bit above the that temprature my torch flame turns a bit jelow orange like when touching the metal, the same way it does on brass and silver. alluminum is an easy material to work with. thanks bill and visitor, anny advise on anodizing Al?

time for another update

chasing
first I fixed the big mask on my small pitch bowel for chasing

chiseling
after chasing I removed the eyes with a chisel.

forging & forming is now almost done. now its finishing and anodizing for a cool collour. again ANYONE with tips for anodizing Al & colour trix?

thnks & grtz ambition out.