Copper is a brownish-orange metal with a bright lustre in its natural state. Since copper corrodes slowly, its functional and decorative uses are many. These uses include statues, roofing trim, electrical wiring, plumbing, downspouts and other building materials. Although beautiful in its natural state, if left outdoors to age in the elements, copper slowly takes on a greenish-blue patina known as "verdigris." This process often takes years of environmental exposure. To hasten the patina process on copper, use household ingredients. The copper will change to a verdigris patina in hours instead of years.
Clean the copper surface with window cleaner to remove dirt, grease or grime, then dry with paper towels. Refrain from touching the copper with bare hands; body oils will repel the solution and prevent the patina from developing.
Mix 2 parts white vinegar, 1 1/2 parts non-detergent ammonia and 1/2 part non-iodised salt in a spray bottle. Shake until well-mixed. The size of the copper piece will determine how much solution to make. For example, if the copper piece is a small candle holder, use 2 tbsp vinegar, 1 1/2 tbsp ammonia and 1/2 tbsp salt for the solution. For large copper planters or statues, use cups instead of tablespoons for the measuring containers.
Spray the vinegar solution on the copper piece until thoroughly wet. Depending on the shape of the copper, the solution might need to be applied several times if run-off is an issue. The copper needs to stay wet with the vinegar solution for the patina to develop.
Reapply the vinegar solution after one hour. Check the patina to see whether it's developing adequately and whether there were areas missed during the first application. The patina will develop faster if the copper stays wet.
Leave the solution on the copper overnight, if necessary, for the verdigris patina to reach the shade of blue-green preferred. When the desired verdigris patina is achieved, rinse the copper with clear water. This can be done at any time during the ageing process.
Atmospheric conditions determine how quickly the copper reaches a verdigris patina. Humid days will help the copper stay moist during the ageing process. For dry arid locations, keep the copper wet by covering with cling film after applying the vinegar solution.
Wear eye goggles if spraying the vinegar solution outside on a windy day and protect your hands with rubber gloves if necessary.