As far as i know, my soldering tip will start to oxidize (or black out) if the temp is over 450C when i left it there, so what i do is take a negative screwdriver and scratch it away. As for quality goes, i have no idea at all, and it might be low quality as well, since i just simply buy it from jln pasar and it has no brand. Last time i got another cheapo soldering iron with its tip completely black out and won't take any solder, i sand away the black stuff with a sand paper, then wrap a few turn of solder wire on it, and turn it on and wait for it to heat itself up until completely melt, then dip the tip into flux. I repeat a few time, now the iron works again.