Why is it important to clean copper fittings before soldering or brazing?

Cleaning copper fittings before soldering or brazing is crucial because it removes oxides that form on the surface of the metal. These oxides can create a barrier that prevents proper adhesion of the solder, leading to weak joints or potential leaks. If the surfaces are not adequately cleaned, the oxidation can interfere with the formation of a strong metallurgical bond, resulting in a less reliable connection.

While it's true that making fittings shiny, removing grease or oil, and improving their appearance are tasks associated with preparing metal for soldering, the primary reason for cleaning is the removal of oxides. Oxide layers can significantly affect solder flow and bonding, thus directly impacting the quality and integrity of the finished joint. Proper cleaning ensures that the solder can flow freely and bond effectively to the base metal, which is essential for creating robust and durable fittings in plumbing and electrical applications.