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Black Spots in Chromic Acid Anodizing

Have problem with minute black spots showing up on chromic acid anodized parts sealed in dilute chromate seal. All tanks are in specification. The spots are only on certain areas of the parts, not on the whole part. When the chromic acid anodize is stripped, the black spots are visible and can not be removed chemically. Looks like a metal condition. Does anyone have any ideas?

Ray Handwerker
- Bensalem, Pennsylvania, USA
2003

What is the alloy? Please tell us the surface preparation. Voltage Ramp?

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2003

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