Making an alloy

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.
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Ted Frater wrote:

sorry, made a mistake its 9 1in cubes of copper to 1 1in cube of tin.
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wrote:

Alloy composition is specified by weight, not volume, so your friend made up the alloy in the proper proportions.
You can locate similar commercially available alloys here: http://www.matweb.com/search/CompositionSearch.aspx
--
Ned Simmons

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It makes a difference if you make the alloy either by volume % or by weight %. It sounds like you made the alloy based on volume % when you should have made the alloy based on weight %: i.e. 9 lbs copper +_ 1 lb tin. If you made the alloy based on 90% volume by weight, you would get 91.7% copper to tin by weight.
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On 9/25/2010 12:08 PM, Ted Frater wrote:

My guess is a processing problem, not a bad alloy mix. The price break in cymbals is generally between cymbals made with 8% tin or 20% tin alloys. 8% tin is available in sheet, and can be punched out. 20% is not available as sheet, as it is too brittle to roll cold. If you view the cymbal manufacturer's videos on Youtube, you will see that the 20% tin cymbals are made from a poured alloy biscuit, rolled flat while still red hot, being returned to the oven to anneal, and rolled more while still red hot. It may be that your friend missed the red hot part.
Kevin Gallimore
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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
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On Sat, 25 Sep 2010 13:59:26 -0700 (PDT), snipped-for-privacy@prolynx.com wrote:

If you search for alloys close to a 90/10 composition on the matweb link I gave, it appears that just a trace of phosphorous has a big effect on formability.
--
Ned Simmons

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Ned Simmons wrote:

Thanks everyone for your help. One never knows it all.
The shield was on a wooden backing, with 1/2 to 1mm thick bronze sheet raised in all sorts of Celtic designs. The sheet would have had to be beaten out cold then raised in the usual way . Ted Dorset UK.
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http://www.bellchamber.net/catalogue/rings/PhotoBatterseaShield.jpg
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