What is the best way to clean the tip of a soldering iron?

Using a wet sponge to clean the tip of a soldering iron after it has reached its operating temperature is the most effective method. When the soldering iron is hot, the moisture from the sponge helps to remove oxidation and any solder residue without damaging the tip. The gentle action of wiping against a wet sponge effectively cleans the tip, maintaining good conductivity and prolonging the life of the iron.

In contrast, other options may not provide the same level of efficiency or can potentially harm the soldering iron. For example, using a dry paper towel may not be effective in removing oxidation and can leave behind debris, whereas soaking the soldering iron tip in water can lead to thermal shock and damage. Lastly, wiping the tip on a metal surface could scratch or mar the surface, thereby degrading its performance or leading to premature wear. Thus, cleaning with a wet sponge is the preferred method for maintaining a soldering iron.