Once you get the wax casting, that has to get cleaned up all perfect, and then a sprue and vent (or gate) system has to be designed and attached to the model. Sprues are like sticks of red wax in varying sizes, with which you create a pouring system for the metal. The metal pours into a cup, through sprues, and the air flows out through vents during the metal pour. So you have to build all that in wax on your wax model. In the picture below you can see a sword I was casting with a cup attached to a big fat pouring sprue, with smaller sprues directing the flow of the metal. Vents are not yet attached in the picture.
Next step is investing the wax model with sprues and vents attached, in another kind of mold, one that can withstand the hot molten metal . I studied this process for nine years in school, running my own little foundry in grad school, and then working at a professional Art Foundry, and I have never seen a mold that can be reused after pouring metal into it. To my knowledge, they all have to broken off to get the sculpture out.
The most common type of mold or investment used for this stage of the process is ceramic shell. I have also done plaster/sand aggregate type investments, and resin bonded sand.
So, you see there is a lot of work that goes into the process. Also when the metal comes out it has sprues, flashing, defects, that need to be ground off.
When I have something cast at a foundry, I make the piece mold for my sculpture myself, and just give them waxes. They will give you a better price if they don’t have to make a mold. I also take the piece back just sandblasted clean, and cut and grind off any extra metal at home. That’s another way to save the workers time and get a better price.
Here is good link about what I’ve been talking about.
Also, a forge is different than a foundry. A forge is for blacksmithing, an entirely different process.
If you want me to come in for a wax workshop I can, just let me know when is a good time!
Tracy
I too would love to participate in a wax carving workshop, and a mold-making one as well. And I would love to learn more about bronze casting.
tl;dr below:
I know someone who's a sculptor, and she talks about the expense of working with bronze - both in terms of the cost of materials, and the cost of operating a forge. She also talks about how incredible it is to work with FIRE and melt metal, which makes it sound really amazing.
There's a fair bit of time involved in preparing the mold for complicated object so that it can be cast properly. The lost wax casting method involves making the wax object, putting the mold material around it, drilling holes in the mold where the metal gets poured in, and then melting the wax out. If you plan to make a one-off piece, you break the mold after pouring the metal. Otherwise, you have to know how to cut it so that it can be removed from the cast object (e.g.if you have parts that fold in on themselves).
I was curious, so I went online to see where one might buy the raw metal for casting. Bronze is apparently about $15/lb (
http://www.mcmaster.com/#red-metal-ingots/=t29up6) from an industrial supplier, but I found it cheaper through eBay (12lb ingots for $90 + $20 shipping from the east coast). It contains copper, which at the moment has a pretty high market value (and is a reason why people steal copper wire, statues, and things). People buy leftover bronze from machine shops, but there are issues with mixing different kinds of bronze alloys together.
Woo!
Anca.
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