yo ho ho and three bottles of rum. we have problems with soldering. using weller 140/100 soldering guns, supposed to heat up and melt solder in 6 seconds. when the tips are fresh, this happens. later, the tips start to turn black, and it no longer works. this may be because we aren't leaving solder on the tips after the work is done. is this true? is there a reliable way of fixing a tip that has gone black? thanks! wiring is proceeding nicely, regularly replacing tips, but that is obviously not a good solution..