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Cyanide spots and stains in brass plating
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I would just ask about a good cleaner in our metal especially in zinc and tin. Because every time we plate bright brass, after painting there will come out a bloody red color and black spots in the metal.
thanks!
chemist - Philippines
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I am not sure that I understood the question, Avegail, but brass is usually plated with a cyanide plating solution and these cyanide solutions are well known to leach out and stain the surface. Try significantly improving your rinsing after plating, including alternately rinsing a sample part in hot and cold clean water. If the sample part doesn't stain, it is a good indication of what you need to do. Trying to clean the stains off of a lacquered part will probably not be successful. Good luck.
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 Ted Mooney, P.E. RET finishing.com Brick, New Jersey |
January 27, 2012
Q. We are plating Cyanide brass as a decorative plating. We antique after brass plating and after brushing; we then do epl lacquer.
Post plating, we rinse in water 3 times, also one hot water dip.
The base metal is zinc die cast components with very good quality casting. Porosity if any is very minimal.
Most often we get black oozing spots (of cyanide). We understand that the cyanide rinsing and passivation is lacking somewhere.
Can you suggest a good drag out process to remove cyanide, since spots appear only at porosity areas; then too they appear after 24 to 48 hours later.
- Delhi, India
First of two simultaneous responses -- January 27, 2012
Neither three rinses nor 300 rinses will remove the cyanide. Try rinsing then dipping in 1/4 to 1/2% sulfuric acid (which must be occasionally changed), then follow your regular process. If it still spots out, then again do the 1/2% sulfuric acid dip, rinse, hot/cold/hot/cold; then hang up on the wall for three days, scratch brush and lacquer.
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Robert H Probert Robert H Probert Technical Services  Garner, North Carolina
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Second of two simultaneous responses -- January 30, 2012
Post brass plating, we need to antique and brush the pieces. We have cyanide bleed-outs after about 48 hours of brass plating. What process of passivation / rinsing is required and at what stage?
i.e. After brass plating or after antiquing.
If we passivate the brass plating, won't it affect the antique dip process ?? How to solve this ?
- Delhi, India
February 24, 2012
Dear Grover,
Let me first know your process sequence for Brass Plating over Zinc Die casting as I have good know-how of various antique finishes.
office equipment - LUDHIANA,PUNJAB,INDIA