Brown Spots on Decorative Chrome
This column marks the end of my eighth year of attempting to give straightforward responses to day-to-day issues that arise in the electroplating arena. It is challenging at times but very enjoyable. All of the questions are real. Yes, I do edit if necessary and change people’s initials to help maintain anonymity.
I have learned that certain questions reappear on a regular basis and many problems and questions are easily answered in the format afforded by this column. Those that are not suitable for use in the column are usually handled via direct e-mail and/or phone discussions. Some questions are such that they can only be handled on a consulting basis. I will continue to respond to questions and problems in a timely manner and with information that can help solve your problems.
We plate decorative chromium on a brass substrate using the following sequence: Copper, bright nickel and chromium. The nickel layer is approximately six microns thick and the chromium is a minimum of 0.3 micron. After approximately two weeks we start seeing white spots, which then turn brown. Do you have any idea what is the cause of these brown spots? B.P.
Based on the photos supplied, I would suspect that the brown spots are corrosion holes. The best way to handle this is to increase the thickness of the bright nickel layer. You might want to consider two layers of nickel: a semi-bright and a bright layer. This would give you better corrosion protection. If you decide to go this route, check with your chemical vendor for suggestions about which plating baths to use.
An overview of decorative and hard chromium electroplating processes.
Masking is employed in most any metal finishing operation where only a specifically defined area of the surface of a part must be exposed to a process. Conversely, masking may be employed on a surface where treatment is either not required or must be avoided. This article covers the many aspects of masking for metal finishing, including applications, methods and the various types of masking employed.
An overview of precious metal electroplating processes.