Originally Posted by Sgtyapd
First of all you need to turn the temperature DOWN on your iron. 63/37 solder melts at 364F, so keeping your station close to 700 makes sense for maximum tip life. If your station cannot solder your application at this temperature you might want to consider a direct power system like the Metcal.
Next, cool the tip down and clean the tip with a soft brass brush, if you have flux charred onto the tip you could try some scotchbrite but start with the least aggressive you can find.
Once it is clean, wrap the tip in rosin core solder.
Power up the system and the flux will activate, and the solder will melt.
This coats the tip and re-tins it.
Now you can wipe the tip on your wet sponge and then retin it.
Re-tin before allowing the tip to sit idle, and for storage.
Turn off the station when you are not using it.
Excellent advice, I was having trouble getting my iron tip to tin, failing multiple times. It seems to be that my Maplin solder was rubbish (99.3 Sn, 0.7 Cu). I went out and got some rosin core and followed Sgtyapd's advice and now I have a perfectly tinned tip! :)
First I used some 600 grade abrasive paper to VERY GENTLY remove the worst of the black, with the soldering iron completely cold.
Then I spent (about 5 - 10 mins) again carefully rubbing the tip on some wire wool, trying not to wear the tip, only remove the black.
I then cleaned the tip with a lint-free cloth and surgical spirit to make sure it was absolutely surgically clean!
I then wrapped the tip in rosin core solder and switched the iron on, ~350C, and waited for the solder to melt.
Once the solder had melted, it tined the tip nicely, I then wiped on a damp sponge and re-tined with rosin core solder.
Voila! Nicely tinned tip again :)