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Removing Yellow Chromate color from a zinc plated part

October 24, 2016

Q. Had some plating done that was to be plain silver zinc, but came back a yellow chromate color (golden color). Is there a way to remove the yellow color without compromising the protective zinc plate and retaining a shiny silver finish? Mechanical removal is out, way too many smalls.

mark hipp
hobbyist - kennesaw
  ^- Privately contact this inquirer -^


October 24, 2016

A. There are two approaches. Technically, the first is best.

1. Many metal finishing suppliers sell silicate sealers such as JS 500, Hyperseal, Superseal, and many others. Dipping the part in this solution (heated) will often remove the color. Usually this is done inline on freshly chromated parts and completely removes the color. This is a great process developed by Jim Sutherland at Torcad in Canada; he's now at Coatings 85. It generally bumps the salt spray protection up to 500 hours or more. Over dried and aged parts this may or not work or may take a long time to removed the color; the corrosion protection is enhanced regardless.

2. Ford used to have a process called "double dip" chromating in which the freshly chromated part was dipped in a dilute warm solution of soda ash and caustic soda to remove the color. This process was used prior to RoHS (IMHO)mania.

tom_rochester
Tom Rochester
Plating Systems & Technologies, Inc.  

Jackson, Michigan, USA



October 26, 2016

thumbs up signI did a little experimenting and found that a 25/75 solution of (sodium hydroxide / 2-butoxyethanol) and water respectively, at 160 degrees for 3 minutes removes 95% of the yellow and leaves a very bright zinc. Don't know if this is chemically correct but seems to work well? Thanks for the help and response.

mark hipp [returning]
hobbist - Kennesaw Georgia usa

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