Black Stains when Brass electroplating onto plastics

A. Kusama,

You need to plate nickel after the copper, because it is the correct method for plating brass on any surface not only on plastics. So, copper, bright nickel, and afterwards brass.

Good luck,

A. Dear sir,

Please specify whether after brass plating on copper surface, you are using a lacquer also on the brass surface? Because brass has the property of getting tarnished very quickly with time in contact with environmental factors viz. moisture, temp, etc., you find black spots on the brass surface. So to protect the brass coating give the plated material a dip in lacquer.

Good luck,

A. Hi. There are many different ways to plate plastic, depending on how high quality and robust the plating must be. Plating of automobile exterior plastics, for example, is much more difficult and much more robust than plating strictly for decorative effect with no wear or exposure. Please see our FAQ on Metallizing Non-conductive Items if interested in that.

But the robust method involves electroless nickel plating anyway. So electroless nickel plating followed by brass plating may be ideal. Sandeep is right, of course, that the brass plating will still tarnish if not lacquered or clear coated. But most brass plating solutions are cyanide based and cyanide staining is a perennial problem perhaps best solved in this case by alternate hot and cold rinsing. Good luck.

Regards,

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A. Hi Edward. I'm confident that people will be pleased to try to help you, but realistically you probably should bring in a plating consultant if your people don't know the subject.

Every electroplating textbook that I know of includes a chapter on brass plating. Most brass plating baths are cyanide based, which means you'll be introducing a powerful poison to your shop that you are not familiar with (unless your silver plating is cyanide based). I would not introduce cyanide without hands-on instruction. There are some cyanide-free proprietary brass plating baths, and you could investigate that.

Brass is usually plated on top of nickel plating; I don't know if you were planning on that. It is also possible to do brass-toned electrophoretic lacquer instead of actual brass plating, but this requires somewhat different equipment.

There are many ways of metallizing plastic. Spraying copper powder probably offers far less adhesion than some other methods, but even here the adhesion is probably much better if the parts have been properly cleaned and pre-treated than if unprepared parts are simply sprayed.

Regards,

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A. Hi again. Modern Electroplating is a pretty good one, and has a chapter on brass plating specifically as well as a chapter on alloy plating in general. The Metal Finishing Guidebook is good too.

Regards,

A. Hi Edward. According to Faraday's Law, the plating goes where the current goes; but the current more or less takes the shortest path. You need "auxiliary anodes" to get good coverage on the interior of the piece. That means either anode material connected to the anodic current, or pieces of stable metal attached to the anode, and positioned in that "shadowed area" so the anode is closer to it than to anything else.

The best decorative effect is probably achieved by plating with the auxiliary anodes first, then going through the plating tank a second time with only the tank anodes.

Regards,

A. Hi again. It is possible to build the auxiliary anodes right into your plating jig/rack, so they are agitated with the rack, and just connect a jumper cable from an auxiliary anode connection point on the jig to the anode bar to allow rack agitation. But it's up to you to figure out what is the easiest method that works :-)

If the only plating you are doing is cyanide brass, the auxiliary anode can probably just be steel, taped or plastisol coated except where you want it exposed. If you are doing an underlayer of nickel plating, you'll need something more exotic like nickel.

Regards,

A. Hi. Again, you really should retain a plating consultant or at least get the supplier of your plating solutions to visit and advise on proper use. Electroplating is a hundred year old trade and you don't need to do absolutely everything by trial and error. We may have been misunderstanding each other, but people don't usually make up plating baths from raw commodity chemicals, they buy the plating solutions from plating industry suppliers.

No, you won't plate out steel if you connect steel to the anodes in a cyanide brass plating bath. But iron plating is significantly more difficult than copper, nickel, or brass; I would not suggest it. Your anode materials are not ideal, but if they're working after a fashion, I guess you can concentrate on more pressing things.

Regards,