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Coating on etched aluminum foil

We are using an aluminum foil that is approx. 10% etched. I know that in a matter of seconds after etching, there is a layer of oxidation formed. My question is that I think the foil we are receiving has some sort of coating on it (on the "margin" of the foil there is a noticeable visible difference...about 0.125" on both ends) as there doesn't seem to be any oxidation evident. Unless this foil is being etched differently than what I think (using rollers and vats of chemicals, which should give you an even etch and not leave the "margins"), does anyone know what if any coating is applied to prevent the oxidation and what it's made from? Unfortunately the company we are getting this foil from is outside the US and isn't really cooperative in this regard. The foil still "wets" like etched foil so maybe I'm barking up the wrong tree here?

Thanks.

Frank Woodcock
Manufacturer - Oneonta, New York USA
October 26, 2008

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Aluminium has a very strong propensity to form an oxide layer and it is this layer that prevents it form corroding away. You may be right that the metal foil has got a different treatment on the edges, but it could be some sort of lacquer or similar surface treatment. You can be sure that the bulk area of the foil will certainly have an oxide coating on it if the aluminium foil is exposed directly to the atmosphere.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
November 6, 2008