Manufacturing Blues

So I’m working on this project and I decide that I need an antique looking plate showing north and I throw together a ‘N’ with an arrow through it and decide to carve it roughly into a block of wood and see if I can’t sand cast it. But because I’m mostly in a prototyping phase (for several things, evidently) I decide to see if I can’t cast just the face of it in a sand mold and not bother with the whole cope and drag. But because I’m forever making stamps or sprig molds for clay, I naturally decide that it needs to be backwards. It wasn’t til I was pressing it into the sand that I realized I was making a positive casting so the original had to be forward. (I flipped the pic just so it would look right… full disclosure, you know). Anyway I decided to go ahead since I had it and it was getting late, and then if it worked, maybe I would cast the cast and have a relief ‘N’ instead of a raised one, as long as it looked old.
But I ran into a few problems. I don’t have a furnace, and my acetylene torch doesn’t have a big enough tip to keep that much metal molten very easily. The casting poured short, probably because I couldn’t keep it hot enough, and I think it’s too much copper. I need to find a source of tin to formulate a good bronze alloy with all the spare copper I’ve got laying around. I melted down some old bronze I had, but I knew it wasn’t enough, so I just made up the difference with copper.
Maybe I should have done aluminum, but aluminum wouldn’t weather the way I want it to. So in the end it may be a good thing that I did make the original wood cut backwards, because I’m probably going to end up using it as a stamp.