ive never heated it personally. I always just added a small pinch of pure citric acid to water. then gently warmed and mixed it. let cool to room temp, threw in my rock and smash it up. most of the time there was no residue left in the spoon I could see with the naked eye. Mind you I never allowed it to air evaporate and instead proceeded straight to IV injection of the cocaine citrate (or acetate if I used vinegar I guess) solution. in my mind I think if this was done without heat you should be able to air evap on a pyrex dish and then reclaim the cocaine salt, but perhaps im out of my league chemistry wise here