How should you anneal mokume gane made of copper and brass, since
the copper should be water-quenched and the brass air-cooled? Thanks.
I anneal it very carefully and let it air cool. No quenching.
1300 F for one minute. Do not quench. In this and other similar
laminates the logic is to lean towards the need of the harder metal.
Bill
Reactive Metals Studio, Inc
If you are talking about material that is already reduced to
patterned sheet just heat and quench or air cool. neither copper or
typical brasses need any special cooling after annealing as neither
have any aging characteristics that would cause hardening from slow
cooling and neither is prone to hot cracking from quenching. There
are only a very small number of brasses that exhibit hardening from
heat treatment and you are not likely to ever find them in front of
you. So like copper brass softening comes from the heating to
annealing temperature and is totally unaffected by cooling rate, so
air cool or quench it does not matter.
James Binnion
James Binnion Metal Arts
How should you anneal mokume gane made of copper and brass, since the copper should be water-quenched and the brass air-cooled? Thanks.
At one point in my life I made lots of brass,copper & nickel-silver
mokume. 18% Nickel-silver had the highest anneal temperature @ 1100F.
My preferred annealing was in the kiln set at 1150F. Time depends on
how thick the metal is. It is going to take longer for the heat to
soak into a thicker piece, so I would try to get a feel for how long
this would take for the pieces I was working on and leave them for 3
to 6 minutes after they were fully up to temperature. Material less
than 2 mm thick I would remove from the kiln sooner. I judged the
temperature by the oxidation of the copper.
Quenching or air-cooling was dependent on how much the material had
been worked. It is always safer to air cool but after mokume has
been sufficiently forged or rolled there does not seem to be much
danger of delamination. Billets thicker than 3/8 inch or about 8 mm I
would prefer to air cool. I know that many craftsmen quench material
thicker than this, but my theory is that a bigger piece is going to
be stressed by the shock and contraction as the outer layers cool
rapidly and stress against the inner layers that remain hotter
longer. If the lamination is in any way compromised this is a
situation that could cause the bonds to break. Another thing I
avoided for this same reason was to leave a thick, hot billet on a
cold anvil to cool. I have seen several layers cooling more rapidly
against the anvil turn black while the top of the billet is still
glowing and then have cracking appear along the boundary of the two
regions. I leave it to cool on a brick or prop it up on several used
bolts to avoid uneven cooling from contact with a heat-sinking
surface.
My billets were especially thick and heavy. Typically 3 x 6 inch
sheets stacked between 1.5 and 2.5 inches thick before forging.
There are some advantages to the larger size. Longer hot-working time
due to greater thermal mass and a greater ratio of usable material to
edge waste.
Something most smiths can get along just fine without knowing, but
that does make a difference sometimes with mokume is that the time
and temperature required to anneal metal changes with how much that
metal has been deformed by forging or rolling. It is actually just
the opposite of what you would imagine. A slightly deformed piece
will need more time or heat to anneal than one that is greatly
deformed. For example if you have two pieces of metal, starting at
the same thickness that are 5 inches long and cold roll one to 5.5
inches long and the other to 8 inches long, the second one will be
much harder from work-hardening. But it will take more heat, either
higher temperature of longer soak time to return the LESS hardened
piece to a fully annealed state. You will also get smaller and more
plastic grain structure if you forge or roll the metal more, rather
than less, between annealings.
Stephen Walker