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How to harden thin copper?


Hi Everyone! This is my first post after being a member for ages,
I’ve finally gotten up the courage!

I have just received my first commission piece for a choker out of
copper. It is a trial piece for a specific costume and the client
wants it made out of 0.5mm copper, hinged at the back, fancy clasp at
the front. He felt that thicker metal would be too heavy. I plan to
edge it top and bottom with round wire to help strengthen it, but I’m
worried it won’t be rigid enough, and being so thin I’m reluctant to
hammer it too much (and thin it even more).

Does anyone have any ideas on what would help harden it?

Kylie Quinlivan


There is no way to harden standard copper except cold work. So not
really any help there but one possibility for you is to use the
copper- chrome alloy (Cu99, Cr1) In the US it is called C182 or
C18200. It has two properties that would be helpful to you. First it
is quite a bit harder than pure copper, second you can heat treat it
to make it even harder. It responds to an age hardening procedure
where you heat at 425 to 500 C (800 to 930 F) for 2 to 4 hours. It
is indistinguishable from pure copper with visual inspection and
patinas well. It is a little more expensive and harder to find in as
many shapes and sizes as C110 which is the most common copper alloy
but it is readily available.

James Binnion
James Binnion Metal Arts


Hi Kylie,

If it’s copper sheet, you might start with a thicker sheet of copper
& then use a rolling mill to reduce it to .5 mm. If you don’t anneal
it you shoild end up with a harder piece of copper.

Good luck!


Copper sterling bi-metal might be a good choice. The Sterling back
would add strength and be better for skin contact. 18ga would be
just right.



Have you tried tumbling with steel shot?

Jo Haemer


I didn’t notice if anyone suggested this - but if you don’t want to
make it any thinner by rolling it through a mill or by hammering, how
about work hardening it by bending? I am thinking you could just roll
it up into a fairly tight cylinder, maybe around a dowel or other
such cylindrical form - then unroll it and roll it up in the other
direction. Do this as many times as necessary and i suspect you’ll
get a fairly uniform work-hardening throughout the sheet. When it is
hard enough for your purpose (whatever that is, I forgot already) you
can flatten it gently and make whatever you want to make.



The following experience might help.

A few months ago I accidentally left an aluminium grill pan in an
oven that I switched to maximum temperature for an hour or so. The
grill pan was made of 0.7mm sheet aluminium and was originally very
rigid. After the accident it was very discoloured with burnt-on
grease, and exceedingly soft. So soft, in fact, that very mild finger
pressure would bend it. Attempts to clean the burnt-on grease caused
major distortion. It was far too soft to be used as a grill pan.

A friend suggested that sand blasting would both clean and harden
it, and since it was totally useless as it was, there was nothing to
lose by trying it.

The result was amazing. All the burnt-on grease was removed, as
expected, and the hardness was restored totally. We were both
surprised by the amount of hardening produced by the sand blasting.
The grill pan is now back in service, as good as new, except that it
now has a matt finish instead of smooth. Not that that matters for a
grill pan.

Regards, Gary Wooding


If it is for a costume, how durable does it have to be? For one
event in the evening or a whole day in a joshling crowd it could be a
considerable difference in how durable it needs to be. Putting a bit
of a dome in a flat surface makes it harder.