Removing AL oxide but not plastic material

[bomscho]

I know one can remove aluminum oxide easily and completely, but this has me stumped.

Here is a layer of oxide so thick it's eaten thru the thin aluminum sheet in some places. something's been reacting on the surface for years. problem is, underneath it is some text from an old printing plate. it's printed on in that mauve plastic ink compound used for printing images onto aluminum which is then used for printing on paper.

you can almost make out the word COFFEE under all the crud.

so: is there any way to remove the crud without damaging the plastic-like printing compound fused into the aluminum? i've tried sodium hydroxide, it wipes out oxide and ink. so does baking soda and Simple Green with light scrubbing. MEK does nothing, neither does denatured alcohol of course. ideas?

[woodjames]

Both hydroflouric and phosphoric are both effective at removing aluminum oxide. Hydroflouric is pretty nasty stuff, whereas phosphoric isn't that bad. Caswell sell phosphoric as ''Aluminum Brightener''. Just be sure to dilute it quite a bit. You can sometimes find it at the hardware store as tile and grout cleaner.

I know one can remove aluminum oxide easily and completely, but this has me stumped.

Here is a layer of oxide so thick it's eaten thru the thin aluminum sheet in some places. something's been reacting on the surface for years. problem is, underneath it is some text from an old printing plate. it's printed on in that mauve plastic ink compound used for printing images onto aluminum which is then used for printing on paper.

you can almost make out the word COFFEE under all the crud.

so: is there any way to remove the crud without damaging the plastic-like printing compound fused into the aluminum? i've tried sodium hydroxide, it wipes out oxide and ink. so does baking soda and Simple Green with light scrubbing. MEK does nothing, neither does denatured alcohol of course. ideas?

[bomscho]

hi james, thanks for the tip. you were right about phosphoric; i found it as "phosphoric prep & etch" in paint sec of home depot, but all 5 jugs were dusty with chewed up stained labels..guess they don't sell much. it wasn't as aggressive as lye, but was still too much so (see attached).

i diluted 1:3, but even hosed off and not scrubbed, this takes off the ink. i'm starting to think there's no way to clean these plates without damaging the graphics .

[woodjames]

Sorry Pal. I don't think that diluting much more will even make the stuff work too much at all without getting it really hot. I'm not really familiar with any other chemical means.

-Jimmy

hi james, thanks for the tip. you were right about phosphoric; i found it as "phosphoric prep & etch" in paint sec of home depot, but all 5 jugs were dusty with chewed up stained labels..guess they don't sell much. it wasn't as aggressive as lye, but was still too much so (see attached).

i diluted 1:3, but even hosed off and not scrubbed, this takes off the ink. i'm starting to think there's no way to clean these plates without damaging the graphics .