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Gold plating color change - tarnish problem

We are having a quick tarnishing problem with our gold plating. We put 1-micron gold plating (using IWG's MC218) over 925 silver material. After micron gold plating we do flash-gold plating for color purposes over micron gold layer.
As we complete the plating process the color comes out ok (14k hamilton color). However when we touch the plated piece around 30 seconds the color changes and becomes a dark orange color. When we steam-clean the piece the color goes back to the original 14k hamilton color. Also if the piece is left out for a few days the color change as well. It looks like an oxidization problem. Our vendor couldn't solve the problem so far and still working on it. But I thought some of you guys may have an idea as well.
Your help will be appreciated.

Regards

Cem Ates
Plating shop - Istanbul, Turkey
October 10, 2010

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October 13, 2010

Hi Cem,

Did you try without 14K flash gold to confirm the problem is not related to thick gold? If the problem is confirmed due to 14K flash gold, then possible causes maybe:

1. Gold conc in flash gold bath is too low or other metallic elements (to contribute the 14K gold color, such as indium, cadmium, iron, copper, etc) concentration are too high and/or out of optimum ratio.

2. Contamination of flash gold bath (organic or inorganic).

3. Poor rinsing/drying after flash gold.

4. Rectifier output (ripple, etc) and/or wrong current setting.

Regards,
David

David Shiu
- Singapore

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An anti tarnish dip (not lacquer) may help.
Regards

T.K. Mohan
plating process supplier - Mumbai, India
October 13, 2010

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Thank you for your recommendations. We discovered that the color change was because of cyanide left overs on the surface. Now we are cleaning the items by washing in water over 80 °C. This is a really time consuming process. Is there any other way you can recommend for cyanide destruction?

Thanks

Cem

Cem Ates
- Istanbul, Turkey
October 24, 2010

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Hi, Cem. I am not immediately understanding why hot water rinsing is such a time-consuming process, but you could try ultrasonic rinsing. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 25, 2010