A quick guide to your first copper ingots, from someone who ruined a bunch

I’ve been running a little test using the copper bar technique you described. My first bar had some definite pitting, but I made a slight tweak to the cooling time after getting it out of the mold. I left the copper resting right on the concrete floor for about thirty minutes after removal. I was aiming for an hour, but noticed the internal temperature was dropping so fast that thirty minutes seemed like a sweet spot for structural integrity without warping too much.

I usually finish my pieces in a small bench vise. Before I did this test, the corners tended to spider out when I tightened it, especially if the metal felt even slightly warm. By letting it reach room temperature first, the bar stayed solid enough to take a proper job. It makes a huge difference when you are trying to get a smooth, round edge. My next pour was cleaner than the initial test, though it took me longer to get the hearth hot enough. I ended up using a couple of extra sticks of propane just to get the ceramic near the right temperature, which was a little overkill, but it paid off. The final bar was much smoother than my first couple of attempts. It seems like the heat retention aspect is more critical than I initially thought for the finishing phase of the casting.

I'd skip the concrete floor part of your test. A slab that's been down a few years holds moisture, and dropping hot copper right on it can flash that water to steam and pit or chip the surface under the bar. I ruined a patch of garage floor that way years back with an aluminum casting. An old baking sheet or a couple of firebricks under the bar does the same cooling job without the risk. Also curious how you were judging the internal temp, since I've never found a cheap way to check that mid-cool.

On the vise part, if the copper is still fighting you even after it's stone cold, give it a red heat and quench it. Old plumber's trick for softening copper, works the same on a bar. We used to do it with roofing sheet back when they still sweat the seams. Air cooling after the anneal leaves it soft as lead, then it takes the edges nice without any spidering. Back in the day we poured into cast iron molds seasoned with a soot lamp, but honestly a torch-warmed steel mold does about the same job if you're patient with it. Your hearth heat observation matches what my old shop teacher used to yell at us, half the bad pours were just cold crucibles.