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  #1  
Old June 21st 09, 05:32 AM posted to rec.crafts.jewelry
Limpy[_2_]
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Posts: 11
Default Math

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.

The obvious answer ain't the one I want. ;-)
--

Anulos qui animum ostendunt omnes gestemus!
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  #2  
Old June 21st 09, 06:15 AM posted to rec.crafts.jewelry
Peter W. Rowe[_2_]
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Posts: 115
Default Math

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.

The obvious answer ain't the one I want. ;-)


The obvious answer (due to your unfortunate wording:
You have x pennyweights of sterling.
If you have x pennyweights of another metal, 14K, 18K, etc, then that would also
weigh x pennyweights. (the same because you specified the same weight.)

Ok. I'm being a wise-ass.

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?

The answer goes like this, and it can be used universally to convert between
varyous materials, be they waxes, metals, plastics, or whatever.

Take the current weight, and divide that number by the specific gravity (or
density, though the proper term is the S.G.) of the current metal or material.

Then multiply that result by the specific gravity of the material you want.

In this case, the S.G. of sterling silver is approximately 10.4 The specific
gravitiy of 14K yellow gold is about 13.1, for 14K white (nickle based) it's
12.6 , and the specific gravity of 18K yellow gold is about 15.6, and 18K white
is about 14.6.

So take your weight in sterling, divide it by 10.4, and multiply the result by
13.1, or 15.6, or the SG of whatever else you wish to convert to.

Also useful is to know that the S.G. of most casting wax is roughly 1. Some
(the ones that float) are slightly less, but not by enough to matter. So to
find the finished weight of a casting in a given metal, you simply multiply the
weight of the wax by the SG of the desired metal. Since the SG of wax is 1, and
dividing the weight of the wax by 1 gives the same number, you can skip that
step. With waxes that distinctly float, add a tad more to the metal weight if
you like. and don't forget, when figuring what you'll need for casting, to add
for sprues and buttons... The final estimate of casting weights have to be just
estimates from these calculations, since the final exact volume of the casting
will vary according to thermal expansion of the mold, and shrinkage of the
castings. But in practice, it's pretty close.

And if you want to get really exact for a specific alloy, I found this on the
Hauser and Miller web site, which also has a good chart of S.G. and other
values.

http://www.hauserandmiller.com/reference/melting.html
They also have a table of comparative weights, such as this metal is x times as
heavy as that metal, etc...

***

HOW TO DETERMINE SPECIFIC GRAVITIES OF ALLOYS

1. Find the reciprocal of the specific gravity of each metal in the alloy.
This is done by dividing 1 by the specific gravity. For example, the specific
gravity of silver is 10.49 and the reciprocal is 1 divided by 10.49 or 0.094966.
2. Multiply each reciprocal by the number of parts per thousand of that metal
to be used.
3. Add the results of the multiplication together.
4. Divide 1000 by this total - the answer is the specific gravity of the
alloy.

Example*:
Find the specific gravity of 14K yellow gold having 583 parts gold, 104 parts
silver, and 313 parts copper.
FIRST FIGURE THE RECIPROCALS OF THE SPECIFIC GRAVITIES:
Fine gold: 1 divided by 19.32 = 0.051759
Fine silver: 1 divided by 10.49 = 0.094966
Fine copper: 1 divided by 8.96 = 0.111617

THEN MULTIPLY:
Fine gold: 583 parts by 0.051759 = 30.128
Fine silver: 104 parts by 0.094966 = 9.876
Fine copper: 313 parts by 0.111617 = 34.956
Total: 1000 75.014

1000 divided by 75.014 = 13.33 (the specific gravity of the alloy)

* The specific gravity for any one karat will naturally vary for each
composition.

  #3  
Old June 21st 09, 07:35 AM posted to rec.crafts.jewelry
ted frater
external usenet poster
 
Posts: 133
Default Math

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.
  #4  
Old June 21st 09, 07:43 AM posted to rec.crafts.jewelry
Peter W. Rowe[_2_]
external usenet poster
 
Posts: 115
Default Math

On Sat, 20 Jun 2009 23:35:58 -0700, in rec.crafts.jewelry Ted Frater
wrote:

So what is it? ,

By weight?
or
By volume?


In every alloy description I've ever read, all such measurements are by weight.
Volume comes into play when discussing specific gravity measurments, only in the
noting that it's the weight of a specified volume of metal (the S.G. is the
weight in grams of a cubic centimeter of the material)

Dealing with volume or other, such as atomic, ratios, though, does sometimes
give some interesting insights.

for example, one finds that 18K red golds (75 percent gold, 25 percent copper)
can be very brittle if cooled slowly, because of an ordered array phase that can
form instead of the usual cubic crystal system. That structure makes much more
sense when you realize that if you figure the ratio of metals on an atomic
ratio, it's about 1:1 gold to copper atoms, and the volume of the two metals
ends up having roughly the same 1:1 ratio (though not quite as close).

With that said, it might be worth contacting the British Museum to discuss just
what their figures mean, and why your friend encountered such trouble. It's
also possible, of course, that ancient smiths simply used methods your friend
didn't try. Perhaps it was formed hot, for example...?

Peter
  #5  
Old June 21st 09, 07:06 PM posted to rec.crafts.jewelry
Abrasha
external usenet poster
 
Posts: 298
Default Math

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.

The obvious answer ain't the one I want. ;-)



You may want to word this differently for others to understand what you
want.

The way you wrote is, the answer is x

--
Abrasha
http://www.abrasha.com
  #6  
Old June 21st 09, 07:06 PM posted to rec.crafts.jewelry
Abrasha
external usenet poster
 
Posts: 298
Default Math

Ted Frater wrote:

So what is it? ,

By weight?
or
By volume?

ted.


Alloy calculations are always given in weight never by volume.

There is a very simple reason for that. Weight can very easily be
determined simply by using a scale. This is also very accurate.

Volume is much harder to determine, since one would have to use methods
like water displacements. And even then this is much less accurate then
weighing on a scale. Especially when quantities are small.

--
Abrasha
http://www.abrasha.com
  #7  
Old June 25th 09, 04:33 PM posted to rec.crafts.jewelry
R T Smith
external usenet poster
 
Posts: 2
Default Math



"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?

  #8  
Old June 26th 09, 03:10 AM posted to rec.crafts.jewelry
ted frater
external usenet poster
 
Posts: 133
Default Math

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.

  #9  
Old June 26th 09, 03:31 AM posted to rec.crafts.jewelry
Peter W. Rowe[_2_]
external usenet poster
 
Posts: 115
Default Math

On Thu, 25 Jun 2009 19:10:41 -0700, in rec.crafts.jewelry Ted Frater
wrote:



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.


Why does this confuse you, Ted? It's clear enough. The ratio is slightly
approximate, Perhaps it varies from place to place in the item. But it's
between 9 and 10 percent tin, and 90 to 91 percent copper. Nothing there should
be confusing. They state there are trace amounts of arsenic and lead, but at
less than .05 percent, those easily fit into the slight variability of the
other stated percentages.

Now this has to be by volume, ie 1 part of tin to 9 parts of copper
make 100%.


Ted, you're correct that it adds up to 100 percent. But where do you get the
crazy idea that this HAS to be by volume? As we told you when you first asked,
alloy calculations and formulas are ALWAYS stated as weight percentages. It's
NOT going to be by volume. This is true not just in metals alloys, but general
chemistry too. Unless some other method of measurement is noted (moles, atomic
ratio, or a volumetric unit is used (such as liters, or cubic centimeters, etc)
weight is the standard way things are measured.

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.


No, actually it won't. Because alloys are described by weigh percentages. If
you use volume, you'll get the wrong alloy, with not enough Tin.


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.


Please totally delete the entire concept of volume from any thinking regarding
alloy calculations. It's not used. And yes, interchanging from one to the
other does screw up stated percentages. This should not confuse you. The
methods of measurement are not simply interchangeable. Stick to weight,
consistantly, and it works. Saying that measuring by weight messes up the
volumetric ratio is talking nonsense. Yes, it's true, but it's a meaningless
observation, because the original stated measurements of the alloy are not
volumetric.


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.


The fact that he couldn't do it using his tools and working methods, no doubt
honed skills developed with other metals, does not automatically mean ancient
smiths didn't have other ways of working that alloy. Since the object exists,
and has that composition, it stands to reason that they knew how to work that
alloy, and your friend, for all his skills, apparently has not figured that out.
This should not amaze you. I've yet to meet any craftsman who actually knew it
all and could do everything, even things he/she'd not done before or had
information on doing.


As yet I dont see a flaw in my logic.


See above...

I repeat. Alloy formulats are by weight, not volume. Period.

As Abrasha pointed out, this is not just convention, it's logical. Just how
would you normally go about measuring an exact volume of a metal componant of an
alloy? Unless you'd forged it into a nice measureable ingot who's dimensions
could then be used to calculate the volume, you'd have a mess. How would you do
it with casting grain, for example? Are you really going to go to the trouble
of measuring displacement of the metal in a vessel of water? Do you think the
British Museum did that to the shield?

Using volume to measure liquids works well, since one can use calibrated
vessels. So we have liters, cubic centimeters, quarts, whatever. It's used for
liquids because it's easy and consistant. But for solids, weight is the easy
and consistant one. Measuring the volume of irregular solids, especially
multiple bits and pieces such as one might be using to mix up a batch of an
alloy, is a royal pain in the backside.. It's not done that way for that
reason.

Peter
  #10  
Old June 26th 09, 08:21 AM posted to rec.crafts.jewelry
R T Smith
external usenet poster
 
Posts: 2
Default Math



"Ted Frater" wrote in message
...
|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.
|

1 unit volume of tin plus 9 units volume of copper don't result in 10 units
volume of alloy when melted together. However, 1 unit weight of tin and 9
units weight of copper could be expected to result in 10 units weight of
copper/tin alloy if evaporation and splatter losses could be prevented.

Also, saying that an alloy has 9 or 10 percent tin/copper ratio content is
NOT the same as saying that there are 9 or 10 percent tin content in the
alloy if there are also other elements mixed in other than copper and tin.
Isn't it possible that the other element or elements, besides tin and
copper, had contributed to the ductility of the alloy in question?




 




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