Unless you clean the tip of your soldering iron regularly, deposits will accumulate to the point where it becomes visibly dirty. Although they are a fairly robust tool, it’s still a great idea to do some regular maintenance and cleaning to improve the life and performance of your tool.
It’s a good idea to inspect the tip for cleanliness before you start any new job. As a rule you should make sure the tip is clean enough that it’s shiny and smooth. Usually all you will need to do in order to get it sparkling clean is wipe it on a sponge or steel/brass wool. However because of the heat endured by the tip, the outer layer of material can oxidize. If this is the case you will need to use a special tip cleaning solution. This is usually a mixture of flux and powdered solder. The flux removes any excess material, while the solder tins the tip. This is a handy and effective method because you can get both tinning and cleaning done at the same time. Tinning your tip is an important step that should not be neglected, as it helps it to more easily accept solder during use.
Once a tip is getting too old re-tinning it may no longer be effective, after a certain point it’s best to simply buy a replacement tip. One sign that a tip might be getting too old to keep using is if its shape has changed considerably from wear and tear. Before picking out a new tip for your iron, check out this article about the different types.
Here’s some additional maintenance advice: