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Tin sterling vs. copper sterling


#1

All,

While waiting to get about refining my cabbing technique,
I’ve been thinking ahead about making my first sterling from fine
silver trade rounds.

I have a Kerr 30 ounce electric melter and a graphic crucible, and I
can use Tufa for my molds. I’ll hand forge the results if I must…
sigh…

But, the question I have is this:

I have heard that artisans in many countries will alloy the fine
silver with Tin (Sn) rather than Copper (Cu) to create .925 pure
silver.

Which is easier to forge and polish, Tin sterling or Copper sterling?

Thanks,
Andrew Jonathan Fine


#2

Tin is more expensive than copper… interesting.

The Australian standards allow any metal (excluding nickel) to be
used to make fine silver into .925 sterling.

Regards Charles A.


#3

FYI see:

http://www.marjaninc.com/MarjanPowerPoint_web.pdf
lots of but not what you wanted–Ask them.

jesse


#4

Hi Andrew,

I’ve never ever heard of using tin in a silver alloy. but i do know
tin to be a major problem as an impurity on silver (from soft
solder). Tin isn’t very soluble in silver so would most likely form
an intermetalic compound which are very brittle and are generally to
be avoided at all costs. silver is used in tin bearing soft solders
though, so that may be the source of confusion. i very much hope I’m
wrong 'cos its always nice to learn something new. I’ll be watching
this thread with interest…

Chris Boland


#5

Hello Andrew,

When the cadmium containing sterling silver grades that were used for
spinning or hand forging because of their improved ductility over
regular sterling silver were being phased out a lot of work was done
by the major silver manufacturers into investigating alternative
additions. Tin was one element looked at but when heated in air tin
forms a very tenacious black/grey oxide which is difficult to remove
with traditional silversmithing pickles. My advice to you would be
to stick with copper and if you have something that requires extra
ductility or ability to forge then increase your silver content up
to about 93.0% to give a more easily formed alloy.

Best regards
Charles Allenden


#6

Charles,

Checking the periodic table, I notice that Zinc is in the same column
as Cadmium, and is far less toxic. I have also played with Bismuth as
a non-toxic lead substitute. How well could either of those go with
silver?

Andrew Jonathan Fine


#7

My sister ‘had’ a silver spoon from Indonesia, circa 1960, that she
wanted me to turn into a ring. I was a little leary of it, couldn’t
say why, but she insisted. So I measured, cut, soldered…what an
ugly piece of greyness! Nothing I have done so far has gotten it back
to a silver look. And it work hardened FAST. I never could get it
fully round.

My mom, who when married to my dad, was in Indonesia and brought
back that spoon, said it was ‘Bonka silver’ which was tin-silver
alloy.

FWIW,
Kelley Dragon


#8

Dear All,

Interesting but does surprise me. I previously understood that from
about 9% tin in silver the alloy would be brittle and unworkable. It
may well work for casts and will likely take a high polish because of
the increased hardness.

Another comment I’d like to make about tin in relation with silver is
that for when soft-solder (lead-tin) has been used it is more the tin
that causes the problems than the lead. So although the tin-silver
(lead free soft solder) is better from a health and safety point of
view, from a technical or metallurgical point of view it is still bad
news on silver pieces. For further reading on the problem of fretting
of soft solder on silver see my publication available on the NMA
website (see section 2 on http://tinyurl.com/2cnaw5b )

Best,
Maickel van Bellegem
the British Museum


#9

Hi Andrew,

Checking the periodic table, I notice that Zinc is in the same
column as Cadmium, and is far less toxic. I have also played with
Bismuth as a non-toxic lead substitute. How well could either of
those go with silver? 

Well you could always try. There are a lot of elements that haven’t
been put into silver. The periodic table is set up in groups.

Zinc is used in some silver alloys already, searching on the net
should bring up some results.

When you are thinking about creating a new alloy, you have to look
at both the properties of the elements. These properties may come
through in your resultant alloy, or another element (or more
elements) may be required to make a useful alloy. Simply adding an
element may not work as expected.

Added to this are the hallmarking standards for your country
i.e…925 silver must have that percentage of silver to be stamped as
such.

Look at the periodic table, and you can see that silver and copper
are very close, tin is also surrounded by potential elements that can
be added to precious metals.

You just need to experiment a little. However caution is advised,
some of these elements give of vapour that is not healthy, like zinc.

Regards Charles A.


#10
Interesting but does surprise me. I previously understood that
from about 9% tin in silver the alloy would be brittle and
unworkable. It may well work for casts and will likely take a high
polish because of the increased hardness. 

A straight mix of up to 20% works well with copper. A straight mix
of tin to silver might not work, maybe the addition of a little
copper would be good.

Without experimentation, who knows.

Regards Charles A.


#11
Well you could always try. There are a lot of elements that
haven't been put into silver. 

I would be happy to bet you that all the metals in the periodic table
have been alloyed with silver. The reason you don’t see much in the
way of metals other than copper alloyed with silver is they don’t
make an alloy that is near as good as the silver copper alloy. Even
Argentium has a significant amount of copper in it. The other metals
either make an alloy that is too soft, too brittle or are insoluble
in silver etc.

James Binnion
James Binnion Metal Arts


#12

Hello to all,

When you are thinking about creating a new alloy, you have to look
at both the properties of the elements". 

This is funny-)) Many attempts are made in order to create another
new alloy and believe me that silver with zinc, bismuth, aluminum,
tin, bismuth… has been considert many years ago!! Fine workability,
good rolling capacity, lower meltingpoint, no copperoxydul formed as
like in copper/silver alloy. Major disadvantages are low density and
SOFT. Bolling temp of zinc makes gastrappes leading to unworkable
metalstructure. Several alloy’s with different percentages of zinc
are tryed. Using 20 percent zinc, shure, go ahead.

Metallurgy is a serious matter and not a cooking recipe.

A (german) book with all kinds of alloy’s can be purchased with many
different alloy discriptions and yes, I have it in my library.

Die edelmetall-legierungen in industrie und gewerbe (precious metall
alloy’s in industry and commerce) written by Ludwig Sterner-rainer.

Anyway, have fun and enjoy -))
Pedro


#13

Pedro,

Haven’t seen you before on this news group, glad to meet you.

I hope you won’t mind my picking your brains. I’ll try to put them
back in the condition I found them :slight_smile:

While I won’t presume to be an experienced metallurgist, I did take a
unit each of organic and inorganic chem back in college way back
during my teens.

I remember a few rules of thumb:

  1. Blended metal alloys tend to take on a blend of the physical
    properties of the elements involved. This is because I thought I
    remembered in class hearing that most such alloys were solid mixtures
    of elements rather than compounds of new molecules incorporating
    those elements.

  2. Elements in the same column of the periodic table tend to have
    similar physical properties as well as the same valence.

  3. Alloys whose elements fill each other’s electron shells tend to be
    less resistant to corrosion.

  4. Alloy mixtures tend to exhibit linear behavior in proportion to
    the elements used. It’s yet again an example of a broad engineering
    principle known as linear superposition.

Therefore, as a starting point, I can reason From 1 and 2, that an
alloy composed of a sequence of elements will have similar properties
to an alloy with one element subsituted from the same column of the
period table.

My goal is to make a machineable silver alloy.

Now, I also recall from the discussion here and elsewhere that tin
had been employed by artisans in some foreign countries in place of
copper, but that too much tin would make the mixture brittle.

I think Bismuth, given it’s non-toxicity, would be an excellent
replacement for either Cadmium or Antimony in silver alloys. And it
turns out that Bismuth is in the same column as Antimony anyway.

So, I would try this as a starting point on my new 100 gram scale:
Silver 94 grams, Bismuth 3 grams and Tin 3 grams.

I’d choose 94% for the silver to allow for error in measurement in
small quantities so that I could still call my silver ‘sterling’.

Pedro, do you have any expert opinion on what properties this mixture
should have?

Thanks,
Andrew Jonathan Fine


#14

Hello Andrew,

Zinc is a suitable addition to sterling silver. It is frequently
added to casting alloys as part of the ‘deox’ formulations. If you
are adding it to be cast into sheet or wire products then at addition
levels above about 2% you have concerns with the zinc content fuming.
Zinc melts at 419oC but boils at 911oC and to successfully cast sheet
or wire in a sterling silver formulation you are usually holding the
metal in the range 1000-1080oC. Interestingly Johnson Matthey in the
1970’s tried to patent the simple silver-copper-zinc formulations as
an alternative to the spinning silver (cadmium containing) grades
then available.

Bismuth as an addition to silver alloys is not something I would
recommend. Commercial silver alloy manufacturers monitor this
element as an impurity and try to keep it at low levels (low ppm). In
part this is due to it having an affinity for iron and so its
presence can cause hard spots in finished sheet products.

With regard to silver-tin solder; typically these are in the range
3-4% silver, balance tin, with a melting range of 221-224oC. They
have a joint strength of about one-quarter of that created with a
typical silversmiths solder.

Best regards,
Charles


#15
Metallurgy is a serious matter and not a cooking recipe. 

Glad I amuse you :wink:

True, mixing other elements with silver and gold has been done, and
is still being attempted, there is still a lot of scope. New
processes, mixing different additional elements that kind of thing.
The devil is in the detail. An example is Ancient Greek black bronze,
we don’t know for sure the right proportions of silver, gold, or
copper that went into making this alloy, people are still
experimenting with re-creating it.

True metallurgy “is” a serious matter, however what we do here is
not that serious (otherwise it’s all we’d ever do, jewellery would be
our hobby not our profession).

However, alloy formula are often referred to as recipes. 10% of this
plus 35% of that, heat for X time, add 55% of something else, cool
in a sealed crucible for 24 hours.

A (german) book with all kinds of alloy's can be purchased with
many different alloy discriptions and yes, I have it in my library.
Die edelmetall-legierungen in industrie und gewerbe (precious
metall alloy's in industry and commerce) written by Ludwig
Sterner-rainer. 

Aw that’s just a tease, putting up a book I can’t anywhere, the book
was published in 1930, is there anything a little more current, that
I have a chance of reading?

Regards Charles A.


#16

Hi James,

You just don’t hear of them, or any other metallurgical studies for
that matter (even though, personally, I would find this fascinating).
At some stage I’d like to do a colour study, with gold and copper
going from 1% gold to 100% gold, same with silver, and the same with
a lot of the other elements, then I would know. Of course if this has
already been done, I would appreciate a link.

The fun for me is the attempt, if the attempt fails, you still learn
something, if the attempt succeeds then we all benefit.

A copper and silver mix, is a time tested product.

Copper combines with a lot of other elements fairly easily, and
silver is pretty close on the periodic table, so it will combine with
a lot of elements also. The difference, and you are very correct in
stating the point, the properties of the resultant alloys are
different.

If you mix copper and tin together you get a very useful and durable
alloy. As long as you don’t go over 12% Sn, then it becomes brittle,
and needs other elements added to it to make it a bit more
forgiving. You can add zinc to copper also, again carefully watching
the percentage of Zn produces a useful alloy. Germanium and tin are
very close and as both of these can mix with copper to form a useful
alloy, logically they can mix with silver also.

There is scope to experiment, say you make a nice .925 with an
element close to germanium, and it’s a little brittle, you could
possible add another element into the mixture to solve that problem.

OR you can find a different technique to combining the elements that
overcome the problems with a new alloy.

Experimenting is something that I believe should be encouraged, and
aided where you can.

Regards Charles A.


#17

Hi Charles,

With regard to silver-tin solder; typically these are in the range
3-4% silver, balance tin, with a melting range of 221-224oC. They
have a joint strength of about one-quarter of that created with a
typical silversmiths solder. 

I was sort of hoping you’d reply. Do you know of any higher silver
tin alloys? I haven’t been able to find any

Regards Charles A.


#18

Hello Charles,

The simple silver-tin solder composition is pretty well stuck in
that 3-4% silver range. If the silver content is increased the
melting point of the solder rises quickly. If you increase the tin
content the fluidity of the solder drops and the joint become more
brittle. So any solder of any practical use has concentrated on a
composition close to the silver-tin eutectic point.

When the lead-free solder legislation came into being in Europe
there was a lot of interest in a solder of composition 10% silver,
87% tin, 3% copper which has a melting range of 214-275C as an
alternative to the tin-lead solders. This was due to its low melting
point and good corrosion resistant properties. However the silver
content (even then) made it much more expensive. This was part of the
reason for the move to compression fittings and push-fit connectors
that all domestic plumbers seem to use these days.

Best wishes,
Charles