As the metal parts on a guitar start to tarnish (usually because of exposure to the player's sweat) you can bring back a good deal of the luster by using jeweler's rouge. This is usually available as round pads, which can be used to buff nickel- or chrome-plated parts back to a nice shine. To be most effective, use this as soon as the parts begin to look dull. If you wait too long, no amount of jeweler's rouge will bring back the shine. Jeweler's rouge is also useful when someone else plays your guitar. Giving the strings a quick wipe with the pad can prevent acid from the player's fingers from tarnishing - or even rusting - your strings.