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What contamination causes yellowish tone for plating with zinc chloride in Hull Cell?

Dear Sir/Madam,
When using HULL CELL plating test for zinc chloride, it usually presents white homogeneous tonality but this time prensents yellowish tonality which is more evident specially when the product to light as some yellow dots to appear and give this color showing a lack of deposit and penetration in the current low density zone, before that, we have a uniform deposit in all current areas and do not present this coating failing.

Our plating formula is as follows: zinc chloride 65gr/Lt, Boric Acid 25 gr/Lt, Carrier 4.0%, Brightener 0.02%, 5 min, 2 amp,AA. Can you tell me what caused it? what kind pollution is this? Many thanks for your attention and looking forward to your commends.

B.regards,

Robert Lim
Plating chemicals manufacturer - Taiwan
2005

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Hello,

I think your bath is contaminated with iron , which turns your solution colour to yellowish, hydrogen peroxide treatment , followed by carbon , then filtration of solution will make your solution clear after removal of iron.

Praven Kumar
- Mumbai
2005