I overcooked e6013 rods. put them in the oven on 500F for 15 minutes. the flux turned dark grey. They weld but require more amps. I'd prefer to not throw them out. My only question is if the weld integrity will be weaker in anyway?
Sail you didn't over cook, I know this is an old thread and should receive more of a reply. 6013 burns much better if dry, warm better still. Try them from the box they will burn like a cell for the first few inches then they calm down. If you are chasing a uniform weld root fillers or cap then warm if not hot is my recommendation. Alan