R T Smith wrote:

"Ted Frater" wrote in message
...
| Peter W. Rowe wrote:
| On Sat, 20 Jun 2009 21:32:00 -0700, in rec.crafts.jewelry Limpy
| wrote:
|
| I know there's a way to do this, but I can't remember how.
| I have x dwt's of sterling silver.
| I want to know how much that weight of sterling will weigh in 14, 18k.
| (snip)
| What I assume you want is to know what the save VOLUME of the other
metals would
| weigh, such as if you have a casting in sterling that weighs x, how much
would
| that same model, cast in another metal, then weigh.
|
| Right?
| (snip)
|
| Heres a question for you Peter,
| whilst were on the subject of alloys.
|
| My friend John Fenn is a master silver smith. Creates miracles from
| nothing with almost no tools.
| Cleverer than me by far.
| He was asked to make a replica of the Battersea shield.
| Being the determined person he is he checked out what the original alloy
| ot tin and copper was.
| According to the analysis made by the British Museum the last time they
| did a detailed study of the shield the tin /copper ratio was between 9
| and 10 %.
| So John being the person he is he tried to purchase this alloy in
| sheet form, 1mm thick.
| It is no longer made by any Co.
| So he desided to make it himself.
| No problem getting pure tin and pure copper, neither a problem for him
| to melt and cast a suitable ingot to start with.
| However often he tried he found it would become too brittle at those
| percentages to forge out into sheet despite repeated annealing.
| By reducing the tin to 6% it worked fine.
| so he and i discussed this problem of percentages of metals.
| If the analysis by the British museum was 10% tin to copper, it had to
| be by volume ie you take for example 10 1in cubes of tin and add this to
| 90 1in cubes of copper.
| However this isnt 10 % by weight is it?
| So to get the final alloy of say 10% by analysis does one go by weight
| or does one go by volume?
| Ie do you take say 9lbsof copper and add 1ld of tin to make the 10lbs or
| 100%?
| We asked IMI who list this alloy tho dont make it anymore and they didnt
| know anyone in their Co. who had the answer when we called.
| Since John had a deadline to finish the shied, for a television
| programme, I had here some 2ft by 4ft sheets of 70 /30 copper zinc I
| sent him and he made it out of that. .
| If you want to finish up with va 10% tin to 90% copper
| So what is it? ,
|
| By weight?
| or
| By volume?
|
| ted.

The individual metal constituents in an alloy are measure by weight, not
volume.
When you have a 12k gold alloy, do you think you have equal amounts in the
volume of gold and the volume of the alloying metals?

In your story, the British Museum analysis may have come up with the 9 to
10% tin/copper ratio, but did it unequivocally say that ONLY copper and tin
were in the alloy?


Ill reply on the basis of memory which is still resonably reliable!.
From what I recall, there were minute ie less than .05% of arsenic and
lead in their analysis.
Now im still confused,because if the analysis is by percent, ie 9 to 10
parts of tin to 90 to 91% copper.
Now this has to be by volume, ie 1 part of tin to 9 parts of copper
make 100%.
So if i start with these proportions ie, 1 part of tin to 9 parts of
copper by volume, melt them together then analyse the alloy it should in
theory come out as 10 % tin to 90% copper.

Looking at it further by weight if i weigh out 1 part of tin to 9 parts
of copper, because tin is a lighter metal than copper, im going to get
more than 10 % by volume.
so when I melt and then analyse by volume its going to be more than 10 %
tin.

Getting back to my friend John he, im sure measured his alloy by weight,
it then would have been a bronze that was not suitable for forging into
sheet from the ingot.

As yet I dont see a flaw in my logic.