AusBonsai

I've got access to a kiln this weekend to anneal a bunch of copper wire.

What's the best temperature to anneal copper, and how long should I hold it there for?

Last time I did it: 700 degrees for 10 seconds (checked and the copper was glowing pink), then water quenched. It turned out ok, but not as soft as the stuff from Japan.

I was thinking 750 or 800 and hold it there for 5 minutes.

Also, is quenching necessary? Or is it only for aesthetics (so the wire doesn't oxidise and turn black)?

Tried searching other sites but most people anneal over BBQs or stovetops so it's less precise.

Thanks!

Im definitely no expert, and can't give specific help on your question other than to say its my understanding that the black formed on copper when its heated is Copper oxide which is toxic. Quenching tends to remove most of it so that when you are handling the wire after it doesn't release toxic dust.

Not sure of the exact annealing temps because I just heat in the fire until it is red. I'd search the internet for copper annealing temps.

Quenching is definitely not needed. I just pull the hot wire from the fire and let it cool at room temp and it is good to use.

I've never annealed copper wire, but I am a plumber and have spent a lot of time annealing copper pipe over the years.

I don't think a precise temperature really matters. Basically the hotter you get the copper the softer it gets, but you also lose a little strength when too hot so for plumbing pipes I've been taught to heat until glowing a dull red, which gives a good flexibility but retains integrity as opposed to heating until bright red. That is for water under constant pressure though so I don't know if it's really an issue for bonsai wire purposes. You really want it as soft as you can get it. I know people that put it in their fires and just leave it until glowing red and that seems to work fine. I agree you can put it into water to clean but you can also just brush the oxide off or wipe with a rag doesn't really matter. I think the problem with some wire I've seen sold in Australia is it's just not annealed enough.

Ended up annealing it at 800C for 10 minutes, then quenched in a water bath.

Nice and soft, no brittleness.

A quick search shows copper melting point at 1083C.
To anneal temps must be around half melting temp (measured in Kelvin) so greater than 405C but annealing takes longer at lower temps so recommended temps appear to be 700-800C. Higher temps are recommended for maximum softening but getting closer to melting temp will cause irreversible damage to the structure and make copper brtittle.
Quenching quicker reduces oxidation to keep the copper bright but as we normally like copper to be dull coloured is not necessary for bonsai wire.

shibui wrote: ↑October 9th, 2023, 8:30 pm Quenching quicker reduces oxidation to keep the copper bright but as we normally like copper to be dull coloured is not necessary for bonsai wire.

The person who helped me anneal knows a lot more about metallurgy than I do, and he said for the gauges we work with, quenching shouldn't make a noticeable difference to softness.

To make copper dull coloured, one could also apply a very diluted spray of lime sulphur (or paint it on). Only something I would do if I had freshly wired a tree about to go into a show.