I get 10-15 firings when melting aluminum with this crucible, for copper i wouldn’t pass 6-7. 5-6 to be on the safe side so it won’t crack while pouring. Never fill it up all the way to the rim.fill 3/4 ideally. When new: Always heat upto 500c for 15-20 mins first time using and then increase to 900c empty for 15 mins or so. then let it cool inside the furnace overnight. Afterwards you can start melting metal and get more firings out of it. Do not bang or drop it. Always heat your prongs, clamps and any other tools that may come in contact with the hot crucible. Always heat your molds to prevent steam explosions. Use protective gloves, shoes, goggles etc….