Blackening Metal

[BCR751]

Anyone know of a way to permanently blacken metal, aluminum in particular?  The solutions I've tried all wear off over time.

Doug

[peteski]

The only permanent solution is anodizing. It can be done in many colors, including black.  Think the shiny black Maglite flashlights. But it could also be done in matte finish. Very durable either way.

 You might be able to find a local plating/anodizing/metal-finishing company (I have one next town over). Unfortunately they do work for commercial outfits so they have very high minimum charge. I used them for few aluminum pieces and it cost me an arm and a leg! Lack of companies catering to general public (with more realistic prices) is that they need all sorts of nasty chemicals do do this process, so there are no mom-and-pop outfits that do anodizing.  Look for companies specializing in anodizing on the Web or in your phone book (if you still have one).   

[SandyEggoJake]

For AL, pickling isn't going to yield a black oxide (as can with brass), but there are a few "tougher than paint" options.

@peteski is right - anodizing may be your best option.  You can do DYI anodizing (see youtube). 

Also powder coating can produce a tougher than paint solution on aluminum, but may build up too think of a layer, can chip off, and as with anodizing, commercial shops likewise charge a high min fee.  But Harbor Freight sells a DIY set up if you wish to give it a try. 

Finally, you can try the old blacksmith trick of carbonized tung oil or linseed oil.  Basically paint it on then burn it off, leaving the carbon.  Not a recommendation, as it typically leaves a sticky reside.  But cheap and easy, and for some items (like tool handles) this sticky reside is a feature, not an issue.

As with any thing, surface prep is the key to proper adhesion.

 

[Kisatchie]

 

Finally, you can try the old blacksmith trick of carbonized tung oil or linseed oil.
 

Hmm... Kiz is an expert
at carbonizing everything
when he cooks...

[mmagliaro]

How much "wear" do these aluminum parts have to withstand?  Are they just going to be handled by humans,
or are these parts going to be rubbing against other parts?

If they are just going to be handled, even somewhat roughly, you might consider electroplating from Caswell.
The sell "plug n plate" kits for about $40.  You can buy the nickel plating kit, and ALSO buy a bottle of their black nickel plating solution.  By mixing the two solutions, you can get varying amounts of blackness to your plated coating.

Since it is over aluminum, you will have to spring for a bit more money and first plate the aluminum with copper using  copper acid/etch bath (which Caswell also sells), and then plate again with black nickel.

So by the time you're all done, you're looking at $80 - $100 in costs.  Not the cheapest solution.  But when you're
done, you will have a plated coating of blackened metal on there.   It can hold up pretty well if you let it plate for a long time (like an hour or even two) to get a reasonably thick plating built up on there.

I've been plating parts on my brass 0-6-0 this way, and I'm very happy with the results and the finish.  Even on drivers, the plating seems to be holding up well (but to be honest,  I've only run them on the track for about 5 hours).

[Santa Fe Guy]

Have you considered trying Micro Engineering Track weathering solution.
I used it for years on my rail however not sure if it will work on Aluminum perhaps others might know.
Just a thought.
Rod.

[jpwisc]

Have you considered trying Micro Engineering Track weathering solution.
I used it for years on my rail however not sure if it will work on Aluminum perhaps others might know.
Just a thought.
Rod.

I've used it for blackening a lot of small parts, from 40LPI chain to brass wire. I will try some aluminum foil tomorrow and see what happens.