So I've been tinkering and playing around with this hobby for a while now. Prior to today it was all aluminum. Today I was going to do my first attempt at a copper melt. I had read that it's a good idea to have different crucibles you use for different metals. SO I ordered this one off Amazon, seemingly pretty highly reviewed and whatnot : https://smile.amazon.com/gp/product/B00FBFUB3U/ I went through the usual prep, an hour in the oven at 450, allow to cool naturally, then an empty run in the furnace up to melting temps, let it cool naturally in the furnace. Afterwards it had a nice "pebbly" surface on it which apparently it normal. So this morning I decide to do my first copper run. I've been collecting copper where I could find/scrap it. Most of this was from a cache of dead ceiling fans I got ahold of, plus a nice sized old copper pipe which was laying around a junk shed at my mom's place. Came up to just under 2lbs total. I load up all the fan copper into the crucible and start up the furnace. It runs for a while and I see the wires starting to compress down a little, so it's melting, yay! I put the copper pipe in (and poking up out of the hole in the top of the furnace) and let it keep going. 5 minutes later the pipe is getting shorter so I watch it melt down into the crucible. Once it's all melted it's got a little junk on top. I sprinkle on around half a tablespoon of borax, as I heard it's good to help get the impurities out. Stir it with a graphite rod and let it cook for another 5 minutes then skim the slag off the top. Things are looking great, and dare I feel almost competent at this... Take out the crucible to pour, all good, red hot crucible with lovely copper in it and pour my first copper: That's post a little wirebrushing, and obviously my sandcasting needs some work... I put the crucible back into the furnace to let it cool with the furnace while I run errands. Fast forward 5 hours. I'm back and ready to put away the now cooled off furnace. I take the crucible out since I figure I'll do an aluminum run tomorrow. When I take the now cooled #3 out of the furnace a sizable chunk falls out of the bottom?!?!?! Now am I right to assume this Crucible's days are done after one melt? Don't really feel safe putting it back in and loading it up with molten metal now. But have any of you guys had this happen on a first run with one? Did I do something wrong? Did I just get a not so great crucible? Was that a crap manufacturer I should avoid? Very odd.