Traan(copper) utensils can develop a dark tone over time and a patina which is desirable to make sure that the pan is in great condition. What should be avoided by you is gray-green verdigris which blacken with time and rust. To retain the shine of your favorite utensil, an easy home method is to stir together lemon juice and salt, rub it in with a cloth, and let it rest. Then simply wash with soap and warm water and dry completely, until warm and shiny. Do not use any hard scrubbers for cleaning.