YOU CAN CAST ACCURATE TIN REPLICAS OF OBJECTS USING SUGRU
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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!