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Not to long ago, I started my ventures into metal casting. My early molds were made of plaster, but I quickly learned that silicone epoxy makes GREAT metal casting molds. Unfortunately, the silicone epoxy I was using was not designed for casting metal, and was too soft and flexible. My early silicone molds were not tough enough for lots of repeated use.
But Sugru, on the other hand, is a very durable silicone mold making material. It makes molds just as good as the silicone epoxy I used previously, except Sugru is WAY more durable, and will make molds that will last dozens of casts.
The cast quality of this skull isn't quite exactly what I'm after, but I was in a hurry. Molds need to be broken in before they with make great casts, so the first, second, or even third castings may have bubbles or vacancies. The skull in the main picture is the second cast. You shoulda seen the first one ;)
Ok, this goes without saying (but I'll say it anyway)...
Casting metal involves the use of butane torches. Butane torches have fire. Fire can burn you. So can hot metal. Got it?
If you want to cast high temp metals, just use the sugru molds for wax, then use the lost wax casting process.
There are several people in the comments arguing about fumes. They have not actually done this instructable, so they wouldn't know. Anyway, if you use solid lead free solder, there will not be any fumes. I know this from experience. Please, though, trust your own judgement and use common sense!
Step 1: What You'll Need
-Object to make a mold of
-Tin Solder (or lead*) Make sure it's not acid core. If you use acid core, you will generate hazardous fumes.
-Something to melt the metal in. I use a piece are firebrick carved into a bowl shape. You could make your own out of Plaster of Paris, or a copper pipe endcap. Do not use clay or ceramic.
*If you use lead, please make sure you are aware of the hazards. The MSDS for lead can be found here.
Step 2: Making The Mold
Gently mold the Sugru around the object; in this case, a small skull bead. Leave a little opening to poor the metal through (see picture two)
Put the new mold on a flat surface and let the it dry for 24 hours.
Step 3: Releasing The Object
Once the object is released, piece the mold back together and hold it that way with a clamp (picture two)
Step 4: Casting the skull
Casting is pretty straightforward: Melt the solder with the butane torch in a crucible of some kind, and poor the molten metal into your mold.
After the metal is cool, you can unclamp and pull the cast of of the mold
Step 5: Results
Take a look at the Buddha on the intro. I Cast that using this same method. The mold I used was just more used and very well broken in.
Here are the pictures of my results: