Green Copper Redux

Question:

Our company plates parts with copper. These parts tend to turn green or black if stored for any period of time. I am told this is an oxidation process and normal for copper. However, our customers don’t like it! The problem seems to be worse in the summer when the humidity is high. Is there anything we can do to minimize this? L.H.

Answer:

This problem seems to generate quite a number of communications each year. As you mentioned in your e-mail, this color change is an oxidation process and is normal. In the art world people will spend megabucks for examples of this process on art objects! This patination process is less desirable in an industrial environment.

There are several solutions. I would suggest starting by incorporating a final rinse of your parts with a solution that contains an antioxidant. The most common material used is benzotriazole. Prepare a solution of 1/2 oz of this material in 1 gal of water. Immerse your parts for 2 min. The solution should be hot. Do not rinse the parts after this step. Look in the Products Finishing Directory and Technology Guide under Tarnish—Preventive Treatments for vendors that sell this type of material.

The second thing you can do is store your parts in a more controlled environment. Perhaps you can store your parts in sealed containers with silica gel packets.