There is one thing that can ruin a crucible quickly. That is putting the heat to it when it has absorbed moisture in it. The steam cannot escape, and it can explode, blowing a chunk out of the crucible.
In a dry studio, with crucibles that are getting used regularly, you can get away with getting them hot without any preparation. But if the crucible has been sitting around and the weather has been damp, it is wise to warm the furnace up a little bit, turn it off, and let the crucible sit there for a while. When I blew my #8, it had been sitting on a concrete floor during damp weather. Now I always preheat a bit, just to be on the safe side.