I wouldn't put it in the microwave. I did this and the microwave started sparking and I had to turn it of at arms length, terrified it was about to explode! I also kept it in my pocket for days on end, and used the radiator idea, none of this worked. Then I just went and bought some new rosin. I bought Pirastro Olive dark rosin. Nice and dark and fairly soft. I use it for my bass and violin. To get rid of the old rosin I just play some really hard slow bow strokes without musical intent, and it all gets dragged/ vibrated off.