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Silver Casting



 
 
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  #1  
Old July 16th 04, 03:41 PM
Jack Schmidling
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Default Silver Casting

I have been thinking of casting a chalice in sliver in addition to making
some broach-like settings. I am set up to do sand casting and can probably
finish the stuff off in the machine shop.

I have a number of 100 oz ingots of .999 bulion to play with but suspect
that one does not want to use pure silver for this sort of stuff.

Can someone provide me with some alloying info to get something like
sterling?

Is this really necessary?

js

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  #2  
Old July 16th 04, 03:53 PM
Peter W. Rowe
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On Fri, 16 Jul 2004 07:40:57 -0700, in ¤ô Jack Schmidling wrote:

I have been thinking of casting a chalice in sliver in addition to making
some broach-like settings. I am set up to do sand casting and can probably
finish the stuff off in the machine shop.

I have a number of 100 oz ingots of .999 bulion to play with but suspect
that one does not want to use pure silver for this sort of stuff.

Can someone provide me with some alloying info to get something like
sterling?

Is this really necessary?

js


Recent threads suggest that it's pointless for us to suggest that sand casting
an item of this size may be less successful than you hope, given that silver is
more prone to problems with shrinkage porosity than some of the other metals you
might be sand casting. But if you use plenty of sprues (or gates, if you like),
and the thickness of the chalice you use as the model is not too thin, you might
get sucess. And of course sand casting is easy enough to try over and over till
it works, at little expense other than the silver itself, so I'd say, "go for
it". Not much to lose if you've already got the setup. Sterling silver melts
at around 1640 F, and you'll want it around a hundred degrees hotter than that
to pour, I'd guess... Be sure to use some boric acid powder or a mix of boric
acid and borax, as a melting flux, to help control oxidation when you melt.
Thin sheet metal forms will be difficult to get to fill well, unless you have
the metal at a seriously elevated temperature when you pour, which can increase
problems with porosity. But if you've already got the setup, then it's easy
enough to try, and of course, any silver scrap you generate can easily enough be
remelted, or sent for refining.

The alloy normally used as sterling silver is 7.5 percent copper, with the
balance being pure silver. Be sure to use good pure copper as the copper
source. i've always used scrap copper electrical wire, which works just fine.
If you want to get fancy, there are proprietary silver alloys out there which
use other than copper, in order to reduce fire scale/oxidation problems on the
silver when casting. These tend to produce a softer alloy than sterling, but
may be worth investigating. I don't know if they are available as "master
alloys which you'd add to pure silver. suspect not, but worth asking. United
Precious Metals is the main supplier I'm aware of for these alloys. As I said,
the exact formula for them is proprietary, so I can't give you that composition.

Hope this helps, and have fun. let us know how it turns out, will you?

Peter
  #3  
Old July 17th 04, 01:58 AM
Ted Frater
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Going down the casing route is good thinking on your part in view of
the soldering problems you have had with fabricating your chalice the
traditional way.
Sand casting will give a most unusal texture to the surface, and using
100 oz of silver would definatelly qualify the chalice for the guiness
book of records.
Would your mantle shelf be strong enough to take this size and weight?
I can easily imagine a gallon of wine in it. Certainly nice to use.
the other option would be to cast a cylinder from the silver, then
turn the whole chalice up in a lathe. Fine silver turns very well.
that way you would achieve the shape and size without any soldering atall.
good lateral thinking.
Youll find using pure silver a much better option to the traditional
sterling .
Ive used it a lot . I had a comission many years ago to make some
paper weights in pure silver. these were 3in in dia by 1in thick. I
recessed the top and fused clear enamel therein 1/4in deep then floated
paillions of fleur de 'Lys on the enamel. . fired them in a kiln till
the siver just started to melt. wonderful effect.
Fine silver doesnt get fire scale like the 925 alloy. To answer your
last question it isnt neccessary at all to alloy silver nor alloy gold.
Pure silver has the most beautiful white colour. When you see sterling
along side it theres no comparison. Same with gold. It has the
loveliest yellow of all metals.
as Peter our moderator has said we look forward to seeing the results
of your continuing efforts.
theres no doubt youll get the results you seek in the end.
All our support for your efforts.
Making broach settings are easier done by hammering the silver into a
die. the bigger the hammer the better. My biggest hammer is 275 lbs.
Takes some handling. I now use this minting technique a lot to make
items of jewellery. Its also easy to make money this way. Id have no
problem making 1pound coins (UK currency) but the trouble is they cost 2
pounds to make. Once the tooling is made(the expensive bit) the
production costs are nominal. Ill give some thought to making a chalice
this way, could be a new development.

Jack Schmidling wrote:
I have been thinking of casting a chalice in sliver in addition to making
some broach-like settings. I am set up to do sand casting and can probably
finish the stuff off in the machine shop.

I have a number of 100 oz ingots of .999 bulion to play with but suspect
that one does not want to use pure silver for this sort of stuff.

Can someone provide me with some alloying info to get something like
sterling?

Is this really necessary?

js




  #4  
Old July 17th 04, 02:17 AM
Jack Schmidling
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"Peter W. Rowe"

and the thickness of the chalice you use as the model is not too thin,

you might
get sucess.....


I would not have given it a thought until I saw the goblet I bought on ebay.
It is from Spain for what that is worth but very thick and a really nice
feeling cup. I don't think there would be any problems casting it in sand
other than the usual take 2, 3, etc till getting it right.

If I had the notion at the time, I could have used it for the pattern but
now it has rubies all over it.

The alloy normally used as sterling silver is 7.5 percent copper, with the
balance being pure silver.....


That sounds easy enough but the other question was, do I need to do this?
Would pure silver present any problems?

js


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  #5  
Old July 17th 04, 02:33 AM
Peter W. Rowe
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On , in øô Jack Schmidling wrote:



The alloy normally used as sterling silver is 7.5 percent copper, with the
balance being pure silver.....


That sounds easy enough but the other question was, do I need to do this?
Would pure silver present any problems?


i'm not really sure. it depends some on your melting apparatus, and maybe luck,
as well as how you sprue the mold. There are distinct differences between
sterling and fine silver.

Sterling is harder than fine silver, and even without work hardening, can be age
hardened (heat treated) to make it even harder/stiffer. Whether this is needed
for your cup to serve well, depends on the cup design. Maybe, maybe not.

Sterling is prone to oxidation and tarnishing (not the same thing. tarnish is
the formation of silver and copper sulphides, not oxides, and happens even when
cold, over time. Fine silver will tarnish too, but much more slowly, and to a
lesser degree. Sterling, however, forms a range of oxides, during heating and in
casting processes, as the copper content forms both surface oxides (a black
scale), and subsurface imbedded oxide layers (called fire stain). These can both
cause problems in finishing a piece.

However, sand casting, especially if you use an oil bonded sand, such as
petrobond, differs some from the usual lost wax investment casting, in that the
sand forms a reducing atmosphere around the cooling metal as the oil burns, while
casting investment, being based on gypsum, which can release a bit of sulphure
compount, can actually make the oxidation problems worse. So it may be your sand
casting will give you cleaner castings in regard to oxides than would investment
casting. Or it may be a moot point, since by the time you clean up the rougher
surface from sand casting, you'll have cleaned up the surface oxides anyway.

My biggest concerns for using fine silver regard melting it, and getting good
castings with it, rather than it's suitability for the final item.

First off, it melts at a significantly higher temp. This isn't like melting and
casting aluminum, or brass. The ease of melting fine silver will depend on your
melting equipment.

Second, fine silver, when it melts, goes from solid to liquid at a single melting
point temp, all at once. Importantly, when it cools, it does the same. This
narrow single temperature at which it solidifies, differs from sterling, which
goes through a slushy temperature range as it solidifies. The difference is that
the sudden solidification of fine silver makes it more prone to having problems
with shrinkage holes and porosity, making proper sprues and gates more difficult
to design.

Also, fine silver has an unusual ability, when molten, to dissolve oxygen from
the air, much like carbon dioxide in a soda. If your melting arrangement does
not exclude oxygen pretty well, then upon solidifying, that dissolved oxygen
comes out of solution, litterally spitting out of the silver as it freezes. This
too can create significant problems with large pores and rough surfaces. Whether
your particular melting setup and the use of an oil bonded sand would sucessfully
counteract these effects, I'm not sure of. On a small scale, using an overpriced
version of petrobond sand called "delft clay", i've had decent results with both
fine silver and sterling, but this was on a small (ring sized) scale. I'd
suggest, if you're set up for it, that a melting furnace may work a lot better
than attempting to torch melt the silver. Wtih a graphite crucible, covered,
melting in a reducing atmosphere, you've better control over gas absorbtion of
the molten metal than you would with a torch. And if your starting with hundred
ounce ingots, you'd likely have some trouble melting that much with a torch in
any case.

Best advice I can give you is simply to try it. I doubt you'd ruin the silver by
trying to cast it as fine silver, and the sand isn't so costly either. Then, if
after a few tries you find it's not working, you can alloy it down to sterling,
and try it then.

Peter
  #6  
Old July 17th 04, 04:44 AM
Carl 1 Lucky Texan
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Ceramic shell casting gives you a chance to include a bit of charcoal to
scavenge oxygen during the 'pour' to assist in preventing oxygen
entrapment in the silver. Plus the surface texture will be smoother than
sand I'd bet.

http://home.c2i.net/metaphor/index.html

fyi

Carl
1 Lucky Texan


Jack Schmidling wrote:
I have been thinking of casting a chalice in sliver in addition to making
some broach-like settings. I am set up to do sand casting and can probably
finish the stuff off in the machine shop.

I have a number of 100 oz ingots of .999 bulion to play with but suspect
that one does not want to use pure silver for this sort of stuff.

Can someone provide me with some alloying info to get something like
sterling?

Is this really necessary?

js



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to reply, change ( .not) to ( .net)
  #7  
Old July 17th 04, 04:44 AM
Abrasha
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Jack Schmidling wrote:


That sounds easy enough


Just do it, ... and you'll find out how "easy" it is.

Abrasha
http://www.abrasha.com
  #8  
Old July 17th 04, 08:19 AM
Jack Schmidling
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"Abrasha"

That sounds easy enough


Just do it, ... and you'll find out how "easy" it is.


I was referring to the formula for sterling.


Adding 7.5% copper to molten silver does not sound like much of a challenge
either.

As far as the whole project is concerned, I have made silver, aluminum and
brass bells just a little smaller than this and the only problem I had was
with the handle so I cast it separately and soldered it on later. I was
planning on doing this with the stem/base of the cup also.

js


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  #9  
Old July 17th 04, 08:19 AM
Jack Schmidling
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Default


"Ted Frater"

Going down the casing route is good thinking on your part in view of
the soldering problems you have had with fabricating your chalice the
traditional way..


You know, if you unfriendly types would read my message instead of reacting
to my name, things would be much more pleasant.

I had not problems fabricating a chalice as I never attempted to fabricate
one and never implied that I wanted to. I bought 6 of them on ebay which
gave me plenty of stuf to futz around with.

Sand casting will give a most unusal texture to the surface....


That's why someone invented the lathe. Sand is more than adequate for
anyone other than a Troglodyte whose most sophisticated tool is a hammer.

and using
100 oz of silver would definatelly qualify the chalice for the guiness
book of records....


Who said anything about using 100 oz for the cup? I said I have a number of
such ingots. Is it not possible just to use some of it?

Certainly nice to use.
the other option would be to cast a cylinder from the silver, then
turn the whole chalice up in a lathe. Fine silver turns very well.
that way you would achieve the shape and size without any soldering atall.
good lateral thinking......


Duh! But why not cast it close to the final shape and save a lot of
hogging?

Youll find using pure silver a much better option to the traditional
sterling .....


Ah.... finally something useful.


Fine silver doesnt get fire scale like the 925 alloy. To answer your
last question it isnt neccessary at all to alloy silver nor alloy gold.
Pure silver has the most beautiful white colour. When you see sterling
along side it theres no comparison......


So what is the point of sterling? Surely not to save a little silver.

Making broach settings are easier done by hammering the silver into a
die. the bigger the hammer the better.....


Where does one get the dies? I can't even find decent broaches.

Ill give some thought to making a chalice
this way, could be a new development.


You might need a real man's hammer for that one.

BTW, one of my neatest cast projects was a whole set of nuts as in the
bowlfull around Christmas time. I used the real nuts (walnut, Brazil,
peanut, pecan, almond, etc as the patterns and cast them in pairs. I also
made a small bowl to hold a complete set. Also put them on key chains and
gave them as gifts. We made them in silver, aluminum and brass and won the
blue ribbon, best of show and $100 at the only art fair I ever went to. We
called the display Aluminart. Funny thing was, while we wowed the judges,
we did not sell a single piece. That was 20 years ago and now the melting
furnace is more commonly used for brewing beer but every once in a while I
get the urge to melt something.

js


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  #10  
Old July 17th 04, 08:19 AM
Jack Schmidling
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"Peter W. Rowe"

However, sand casting, especially if you use an oil bonded sand, such as
petrobond.....


That is what I use.

My biggest concerns for using fine silver regard melting it, and getting

good
castings with it, rather than it's suitability for the final item.


First off, it melts at a significantly higher temp.....


I thought copper melted at a significantly higher temp than silver?
Wouldn't this increase the melt point of silver if added?

The difference is that
the sudden solidification of fine silver makes it more prone to having

problems
with shrinkage holes and porosity, making proper sprues and gates more

difficult
to design.


I guess ignorance is bliss as I never had any problems with it in the past
but never made anything quite this big either.


I'd
suggest, if you're set up for it, that a melting furnace may work a lot

better
than attempting to torch melt the silver.....


Wouldn't think of using a torch. My furnace will hold a pretty good sized
crucible. I forgot the number but it is about 8" and 4" in diameter. The
last time I did silver I cut one of the ingots in half so it would fit and
melted in a reasonable time. The only thing I have a problem melting is
pure copper but there is not much call for that anyway.

Best advice I can give you is simply to try it. I doubt you'd ruin the

silver by
trying to cast it as fine silver, and the sand isn't so costly either.

Then, if
after a few tries you find it's not working, you can alloy it down to

sterling,
and try it then....


Sounds like a good approach. I had the noting that it was too soft for this
sort of thing but I am certainly not looking for extra hassle.

js


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