The Big Mess of Wires Blog takes on making metal objects via sand casting:
Today’s project: metal casting! I’d been wanting to try this for years, because who doesn’t love playing with molten metal? This was a single-sided open air sand casting process, which is about as simple as it gets. You basically just press an object into some densely-packed sand, remove the object, and pour metal into the resulting sand cavity. Humans have been doing this for thousands of years. Easy peasy, sort of.
This project was a long time coming. I discussed some metal casting ideas last year, and acquired some equipment. Then everything sat on a shelf gathering dust for 13 months.
I used pure bismuth for the casting: atomic number 83 on your periodic table. Bismuth has a pretty low melting point of 521 F / 272 C, easily reached with an electric heater. The objects here are a quarter, a silver dollar, a wire nut, a DB-19 connector, and a teddy bear pencil eraser. A major limitation of this particular process is that the object must have parallel or tapered sides so you can remove it from the sand without disturbing the cavity you just made. That’s why the teddy bear looks like it’s embedded in a rock: I had to dig it out of the sand instead of lifting it out cleanly. This process is also limited to making one-sided reliefs instead of full 3D objects, because the back is just a molten pool of metal directly exposed to the air as it cools.
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