Although copper is a beneficial nutrient when consumed in miniscule amounts found in food, it can be toxic if leached from copper kettles and pots through cooking. Copper kettles are safe to use if they meet certain criteria.
Old Unlined Copper
Antique or used copper kettles that have no protective lining of aluminum or tin are dangerous to use for cooking or boiling water. The chemical reaction with water or high acid foods like tomatoes or citrus fruits may be tasteless but can cause stomach or digestive system problems.
New Copper Kettles
Most copper pots commercially produced in the United States are thinly lined with nickel, stainless steel or tin to create a barrier with the copper surface. These kettles and pans are safe to use for any cooking or baking application.
Since copper is highly sensitive to air and easily discolors, manufacturers frequently coat it with a thin layer of lacquer to keep it attractive during storage. Remove this coating with an acetone solution before the first use to prevent the copper from turning black permanently upon exposure to heat.