WHAT I'M MELTING
One of the big items when I first started doing this was cans. At my former place of employment, I took several trashbags full of aluminum soda cans. I was responsible for emptying the recycling can, so I recycled.
After retiring, that source dried up, but as I began to sort through "stuff" I'd accumulated in the garage, I realized that a lot of the stuff to be disposed of contained aluminum.
Something else that hadn't seen the light of day for a long time were a lot of old brass plumbing fixtures that I accumulated over the years.
I've experimented with a couple different types, because aside from melting metal, I wanted to be able to forge steel.
My first two forges I made using metal buckets lined with the appropriate materials. My first attempt wasn't very good, since it was too small and the materials which I had at the time did not hold up.
The second attempt has served well. I used a larger bucket, and lined the bottom and sides with boiler fire brick. A hole in the side allows me to direct forced air through the coals.
I still had enough fire bricks left to build a slightly larger forge. While the larger bucket forge is good for forging smaller pieces of steel and melting small amounts of aluminum, I use the brick forge for larger projects.
CASTING ALUMINUM AND BRASS
I'm using the lost foam process for casting. I carve the item I want to make out of styrofoam, set it in a mixture of "green sand", a mixture of silica sand and clay. When the molten metal hits the styrofoam, it instantly burns away, and the metal takes its place.