I bought an espresso machine a little while ago. The attachment that holds the coffee grounds is/was a cup made of bright, form cast aluminium.
A couple of weeks ago I put this cup into the dishwasher; it seemed like a good idea at the time.
Now, the entire cup is black, and coated with fine black flour like powder. The powder wipes off easily, but will not go away. The more I wipe it off, the more of it is formed. Evidently, the highly alkaline environment of the dishwasher stripped the protective oxide coating from the aluminium.
I would like to restore the cup to its original shiny metallic finish, and get rid of the black powder. But have had no success.
I have tried scrubbing with fine steel wool; this restores the metallic finish, but overnight it reverts to the black powdered surface. Similarly, with scrubbing and soaking in water, vinegar, borax and hydrogen peroxide.
Does anyone have any ideas as to how I can fix this and restore the original shiny metallic finish?
Thanks in advance.
I kinda think you’re screwed. Typically, the sort of thing you’ve got is cast from aluminum alloy and clad with a thin layer of pure aluminum, which then forms a very thin oxide layer that is very hard, but not everything-proof. Once the aluminum layer has been penetrated, the alloy is subject to corrosion. I have also read that some dishwasher detergents can react with aluminum, producing hydrogen atoms. Those will migrate through the aluminum until they link up with other hydrogen atoms, leading to the formation of gas bubbles which weaken the structure of the metal, causing it to flake off.
Cascade suggests soaking discolored aluminum in cream of tartar solution, 2-3 Tbs to 1 quart of water, for 15 minutes. I don’t know; maybe this can passivate the surface, but I doubt it.
Autosol metal polish should work however it could be cast zinc ? steel wools way too abrasive try grey scotch brite , then Autosol with a soft cloth.
There are automotive products that can polish aluminum to a chrome finish, and one kind of sealer (NOT A WAX) that chemically bonds to the aluminum surface and prevents further oxidation.
Ask someone in Pep Boys, Autozone, etc for advice.
Are you sure it is actually made out of aluminum? Because I haven’t ever heard of this happening to aluminum, since it forms a protective oxide layer immediately on exposure to air - it just isn’t thick enough to affect its optical properties. Now, it can be made thicker and will look black (anodized aluminum) but it is a hard rigid film, not a powdery substance (it can be damaged but won’t just peel off), which is why aluminum doesn’t rust away under normal conditions, unlike iron. Perhaps it is some weird aluminum alloy, or something that just looks and feels like aluminum.
Thanks for the responses above; I tried all of them except the “Shineseal”, which was not available at any of my local auto accessory stores.
And no, I am not certain that the material is aluminum; I just assumed it is from its appearance and the fact it is very light for the volume of metal.
None of the suggestions noted above had the desire effect, so I bit the bullet and phoned the service department of the manufacturer and ordered a new one. $20; problem solved.
Thanks to all those who had suggestions to offer.
While not relevant to the OP, I thought this article on mercury causing aluminum to fall apart was interesting, in particular because it forms the same black powder described by the OP (no, not saying that the OP’s dishwater is contaminated with mercury).