First melt done, and I'm officially hooked

I did a first pour of brass scrap last spring and ran into the same thermal issues you described. I ended up using a refractory brick layer under the crucible instead of just preheating it, and that made a huge difference when the charge started going liquid. The uneven heating of the crucible seemed to be causing some stress cracks before the melt even started, which was frustrating. My biggest hurdle was the molds themselves. I decided to use rebar and a couple of heavy-duty wooden forms instead of a steel mold, because the heat transfer seemed too rapid with the steel. I lined the wooden box with graphite powder first, and that kept the temperture more stable during the pour. It makes the initial pour feel less frantic.

I found that once I had my brass molten, I needed to skim aggressively. Even with scrap, there's enough oxidation to create a nasty layer on top. I used a long metal ladle to scoop out the scum before I even touched the mold. I ended up with a pretty decent casting, maybe three or four pounds, but the process definitely takes longer than I expected it to. It's a slow burn.

For the next run, I'm going to try increasing the mold size, maybe targeting a larger billet to make the setup worth the extra time.

I went a different route with my fuel budget. Started out wanting to melt copper too, but after a couple sessions with my little 6kg propane furnace I realized copper was eating tanks way faster than I expected. Switched to aluminum for a while, mostly old pistons and lawn mower parts, and suddenly a 20lb tank lasted me through several pours instead of one. The melt point difference is just too big to ignore on a hobby budget. The other thing that changed my results was switching molds. I was using steel at first and getting crummy surface finish, then a guy at our local makerspace talked me into petrobond sand flasks. Now I can make actual shapes instead of lumpy bars, and it's way more fun.

Also started keeping a little logbook, temp readings, how long each melt took, weather even. Weird how much a cold breeze slows the whole thing down. My notes from last November saved me a lot of guessing this spring.

I've got to push back on the wooden forms idea. Steel ingot molds are what most folks use and they work fine - sticking and cracked surfaces ussually come down to pouring into a cold mold, not the steel itself. I warm mine up on the furnace lid for a few minutes before the pour and the bars drop out clean every time. Wood lined with graphite just sounds like char and trapped moisture sitting next to molten metal. Has anyone acutally gotten repeatable results with wood forms, or does it only work once?

Copper was giving me a crusty, lumpy surface on every bar until I started tossing a pinch of borax in right after the charge went liquid. That was the whole game changer for me. The slag went from stubborn chunks to something I could push to one side with the skimmer in a couple passes, and the tops of my ingots came out way cleaner. Cheap stuff too, I just grab it at the grocery store baking aisle. Curious if your copper came out with much of a dross problem or if your scrap was clean enough to skip it.