New solder is generally bright and shiny, like a brand-new dime. Sometimes, however, you might not want your solder to look new. For instance, the appearance of a new soldering job can draw visual attention away from other aspects of the work.
Pour a small quantity of lemon (or lime) juice into a small cup.
Use a hairdryer to warm to soldered joint. Do not hold the hairdryer still in an attempt to soften the solder; simply get the solder warm.
Dip a small paint brush into your lemon (or lime) juice and paint it onto the warm solder. Let the juice cool. Do not wipe it off.
Repeat Step 3 if the soldered joint still appears too fresh.
Leave the lemon (or lime) juice on the soldered joint after it has dried.