When leaving the copper to soak, do not cap the bottle tightly. The gases produced during the chemical reaction will cause pressure to build inside the bottle. Also, make sure to clearly label the bottle and store it out of reach of children or pets. Copper coins can be used as well. Make sure the coin’s content is largely copper; for instance, United States pennies made after 1982 are only 2. 5 percent copper. However, pennies made before 1982 are 95 percent copper.
