I'm not suggesting this is the safest way on earth to make silver
castings with no specialized casting equipment, but we used to:
Nail the lid from a marshmallow creme jar to a 4x4 block (so it sits
like a cup on the end of the block). Use a block of wood about 8
inches long. Pack a wad of wet paper towels in the jar lid - this
will make steam when held down over the soup can.
Cut the top and bottom out of soup cans (these are the hi-tech
investment flasks). Invest the wax as if you had a vacuum machine -
leave a reservoir at the top to pour the silver in. Prop them
upside down on nails in the kiln and do a normal burnout until the
edges of the investment are no longer showing greying.
We torch melted the silver in a crucible and poured it into the
reservoir, really quickly popped the marshmallow lid steam maker
over the top of the soup can, and the steam would push the molten
silver into the investment.
I've since bought a vacuum caster, and to be honest, the casting
quality is about the same. You are limited in size when steam
casting - one ring or object per can.
You can get really badly burned by steam - I come from a pottery
background (I was used to raku) and had good safety equipment
(including fireproof gloves, good tongs, extinguishers, etc). We
always did this in the driveway (gravel). This is dangerous -
remember what your mother always said, "If all your friends jumped
off the bridge, would you...". Use your own judgement about what is
or isn't safe, but please don't get hurt.