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7075 is grey in color after clear anodizing

I have a 7075 plate that an outside vendor has clear anodized and the appearance is grey in color. Looks to me like someone painted the plate with grey primer. Anyone help with why this is happening?

Dale Rhinehart
- Charleston, South Carolina
2005

2005

7075 at 70 °F with 165 to 180 gm/L sulfuric acid, 16 volts should come out clear.

Conditions that will make it come out gray include: lower temperature, higher current density, lower acid concentration, heavier thickness. In January and February on Monday mornings many job shop anodizing solutions are very very cold and that will make a gray color on 7075. Also dirty acid that contains iron will casue a gray color. We recommend electronic grade sulfuric acid.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

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