ATM my bass is in for repair and I'm currently borrowing the band's bass. It came with an old abandoned tub of Pops rosin. It had probably been dropped while cold and had a lot of jagged edges and a large lump had come loose. With nothing to lose I popped (pun intended) it in the microwave for 30 seconds. Seems to have done the trick. The lumps are all one and its a nice smooth clear whole again. I'm sure this is probably well know to many but I thought I'd share.