Re: alloying


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Posted by joewizard on January 04, 19100 at 01:03:11:

In Reply to: Re: alloying posted by Lyle Landstrom on January 03, 19100 at 15:05:21:

Thats a real handy trick. Thanks. I'll try it out next time im over there. I have some silver nitrate i made a while back as an ingredient to silver plate some glass.

Actually, I dont mind destroying a few small crucibles, as I make them myself, and money gets wasted around here on things that are no where near as much fun.

For those who are interested in trying this, ill tell you what i do.. Making one's own crucibles is thought by some people to be pretty dumb.. take it for what it's worth:

About a 50/50 mix by volume of Lincoln 60 fireclay, and 36 grit silicon carbide makes a strong crucible with good heat transfer.

They are a bit porous, especially with the 36 grit silicon carbide. Finer meshes are more expensive, but i guess the finer the better as far as less porosity goes. But this is adequate for my uses.

This one i have in front of me holds about 1 pound of aluminum and has a wall thickness of a bit over 1/4 inch. The cup is about 3 inches wide, and 3 inches tall. Somewhat larger sizes are ok. My biggest one is about 5 inches across the top and thicker.

Make a plaster mold of the outside cup-shape, and give it some draft..(tapered slightly so you can get the dried clay out easily). Include a smooth pouring lip and think about anything else you may want.. maybe a rim for ease of handling with tongs. Get too fancy and you might need a 2 or 3 part plaster mold to get the thing out of there. Keep the section thickness even, and round off sharp corners inside and out.

Mix the dry ingredients. Add a little water and mix to a pasty cream. The plaster, if its dry, will absorb water fast, so wet the plaster mold first. If you have to play with it too long, the clay will dry out. Cracks may appear. If that happens wet a finger and smooth it out. Push a pin through the bottom and sides to estimate thickness, then smooth over the tiny holes it left.

Leave it alone till it dries and shrinks away from the plaster. Then carefully remove it to air dry completely. Might take a day or two or more. Put the dry cup to your cheek. If it feels cold, its still wet. Drying slowly and properly is vital to avoid internal and external cracks in the finished crucible. Dont hurry with this part.

Once dried, it can be put in a kiln and fired. I start in a cold kiln, get it up to about 2200F or 2300F in about an hour, and let it stay there for maybe 30 minutes, so im sure the heat has soaked through the thickness of the cup wall. Shut down and let it cool to room temperature. Any book on ceramics will have more detailed instructions if you run into problems.

However big you make one, visualize it's bottom cracking off at the worst moment. Fear is a good thing to have. Be careful.

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