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#1
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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 -- PHOTO OF THE WEEK: http://schmidling.netfirms.com/weekly.htm Astronomy, Beer, Cheese, Gems, Sausage, http://schmidling.netfirms.com |
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#2
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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
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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 |
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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 -- PHOTO OF THE WEEK: http://schmidling.netfirms.com/weekly.htm Astronomy, Beer, Cheese, Gems, Sausage, http://schmidling.netfirms.com |
#5
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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
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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 -- to reply, change ( .not) to ( .net) |
#7
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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
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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 -- PHOTO OF THE WEEK: http://schmidling.netfirms.com/weekly.htm Astronomy, Beer, Cheese, Gems, Sausage, http://schmidling.netfirms.com |
#9
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"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 -- PHOTO OF THE WEEK: http://schmidling.netfirms.com/weekly.htm Astronomy, Beer, Cheese, Gems, Sausage, http://schmidling.netfirms.com |
#10
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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 -- PHOTO OF THE WEEK: http://schmidling.netfirms.com/weekly.htm Astronomy, Beer, Cheese, Gems, Sausage, http://schmidling.netfirms.com |
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