Q. Our company produces pendants and other jewelry parts out of Zamak metal. We find that the finished products have pores that we are unable to cover with the copper plating that we apply. Can you suggest any processes that will cover these pores? —E.C.
A. The quality of Zamak alloys vary greatly. They can be made from good-quality zinc, aluminum, copper and magnesium, or from lower-grade recycled materials. This variable can affect the quality of the finish that is applied to the parts. The actual cleaning and plating cycle also has a major role to play in finishing the parts. Many different procedures for plating of Zamak have been used, and the table below offers one basic sequence for plating:
|Electroclean||Cathodically or, better, cathodically and finish anodically|
|Dip in sulfuric acid solution||5 mL H2SO4 in 1L water, 30-60 sec. or until gassing begins; do not overclean|
|Cyanide copper strike||Introduce "hot" at ~ 24 ASF for 2 min. and then reduce to 10-12 ASF for 5 min.|
|Dip in sufuric acid solution||Use a 10-mL/L solution|
|Acid copper sulfate plate||Plate to a thickness of at least 10-15 microns. If the part is large enough and you have a heavy enough copper plate, the part can be buffed to smear out the copper and fill in the pores.|
|Proceed with silver plating process||Remember that silver should not be plated directly on copper. A barrier layer should be part of your process.|