How To Anodize Aluminum Black. When we analyze the sample we got the same chemical composition in the good and defected area. Those spots will not be shown before anodizing;
Both are essentially inert in this chemical. After hard anodize, the part may be machined, ground, honed, lapped or stripped to remove areas of the coating. To cut, use a circular saw or jig saw fitted with a saw blade designed to cut sheet metal (fine tooth blade).
The hardness is very low in these spots.
For instance, black dyed type iib anodize will be grey at best. Optical black anodize / martin black. These sheets and bars are anodized on one side, then covered with a protective film. Use 6061 or 6063 aluminum cathode at a ratio of 1 to 3 times more part area than cathode area.