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What etching concentration should I use?

 

GO PATRIOTS (sorry Rams)

I need to educate myself a little bit more about the Etching process. Specifically, what concentration of sodium hydroxide should I use to etch anodized Aluminum and how do I measure that concentration. Is there a point where the etching bath needs to be discarded from buildup of sludge? Is there a good reference source for an amature?

Thanks,

Bruce Jacobson
- Princeton, Massachusetts

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Bruce, as a fellow New Englander, I must also say GO PATRIOTS! Eat your heart out, Rush Limbaugh, we're the best, got it?! As per the aluminum etching solution, there are many suppliers out there who would be more than happy to help you with that endeavor. The usual aluminum etching solution is made up of 5 - 12 ounces per gallon of sodium hydroxide, combined with a chelating compound, usually sodium gluconate or the like. The solution is usually heated to between 140 - 160F. To analyze the etchant solution, volumetric titration against 1.0 Normal sulfuric acid solution with phenolphthalein [on eBay & Amazon] indicator is the norm. By using a potassium fluoride [affil links] solution in a second identical sample, you could determine the concentration of suspended aluminum in the aging bath, then discard the old bath when the Al+ reaches about 10 oz/gal. If you would like more specific info, let me know by making another entry on this letter. I'll miss Drew Bledsoe, but Brady is kickin'!

Randall Fowler - Fowler Industrial Plating, LLC
Cleveland, Tennessee, USA