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Q. We are using a cyanide-based copper plating bath to plate a bell-shaped fitting with ½-inch and 1-inch diameters. We are seeing dark brown stains in the area where the 1-inch diameter is reduced to 1/2-inch. Do you have any idea what the problem is? —M.T.
A. First, I suggest you determine if the stains appear when the parts come directly out of the plating bath or if they appear after the final step in the plating process and are allowed to dry off. Without the part in hand or a photo of the part I cannot give you a definitive answer. Quite often staining of the type you describe is due to poor rinsing and drying of the parts after the plating step is complete.