On Sep 25, 10:08*am, Ted Frater wrote:
Ive a friend that is making a replica of the Iron age Battersea shield,
found in the river Thames in Victorian times.
* Now he and I have been discussing his problem . That is the original
alloy used was copper tin 90/10. by percentage anlysis.
In other words 9 parts of copper to 1 part of tin by volume
* Now he made up his alloy by weight . ie say 18 0z of copper to 2 0z
of tin.
He carefully melted the copper and added the tin, cast his ingot,
cleaned it up and proceeded to hammer it out into sheet.
It always cracked, despite repeated annealing.
So I said *because tin is lighter than copper your in fact adding more
tin than 10%.
If you want a 90/10 to finish up with, you have to do the alloying by
parts. Ie volume .
I said you need say 9 1in cubes of copper to 1 1in cube of copper to get
the 90/10 result. He couldnt see that.
* Now I put this to the scientific minds on REc. Crafts. Metalworking to
resolve, one way or another which is the right way to make this alloy.
* This is not a scam or a troll.
What eventually happened as he had a deadline to finish it I gave him
som 70.30 brass sheet that was the same colour and was ductile enough to
do the replica.
Ted
Frater
Dorset
UK.

Chemical analysis is always done on a weight basis, your buddy's
alloying methodology is correct. What may not be correct is
manufacturing technique. Do you know FOR SURE that such an item was
manufactured by cold-working? Is there any proof that it was done
that way? Frequently this is where modern attempts to exactly
reproduce antique items go wrong. A lot of this knowledge was never
written down, was passed on only from master to apprentice. Sounds
like that alloy is cold-short, might either need casting to exact
shape or hot-worked or cast AND hot-worked. Lost wax would probably be
the way today. Brass and copper-working techniques don't necessarily
translate to other alloys. Also, trace elements can do odd things to
cuprous alloys, how complete was the original chemical analysis?
Thinking arsenic, tellurium, selenium and maybe silicon and
phosphorus. Might have silver and gold, copper refining wasn't that
advanced to remove all traces of those, but those shouldn't do a lot
to the alloy properties.

Stan