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Touchup on anodized aluminum

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Is there a way to touchup a black anodized part(sulfuric) that has had the finish worn off in a spot or two? I don't want to re-anodize the whole part again if it can be avoided.

Jimmy Dickard
- Easley, SC, US


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It depends on what specs, if any, you have to meet. And it depends on what wear resistance you need in the repaired area. But, believe it or not, many people accept touching up with a black magic marker as perfectly valid.

Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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Theoretically YES, practically NO. You will have to clean off, probably mechanically, all residual anodic oxide, make contact, deox briefly in Nitric Acid (some proprietary deox will work, others will attack the other anodized and dyed areas), put back in the anodizing tank and set the voltage for the alloy, redip in dye, seal in plain hot water.

I have done it, it is difficult.

Editor's note:    
   Mr. Probert is the
   author of
Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina



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A possible solution may be to brush anodize the bare spots. Connect the positive wire to the work, the negative wire to a cathode wrapped in felt,(ensuring the usual electrical safety issues are addressed)then wet felt with electrolyte, and brush over the bare spots. You must take into account the thickness of the felt, due to the possibility of arcing. This method is used to colourfully anodize titanium, so maybe it could be of some use to you.

Apparently a well bristled chip brush will hold a nice little piece of cathode up inside the centre of the bristles, using the power lead as a fastener. Trim bristles to appropriate length, allowing a decent gap.

Good luck!

Jeff Swayze
- Kelowna, B.C., Canada

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