# Blackening Aluminum



## tjb (Mar 16, 2021)

Anybody have experience blackening aluminum?  I'm working on a project that will have a part that needs to be black (or close to it).  The part will be made out of 6061T6 aluminum; it will be about 2-1/2" long, 3/8" diameter round stock, knurled on one end, bored and tapped on the other.  I could paint it, but it will be handled fairly regularly, so I'm wondering if blackening would be better.

I've never tried to blacken aluminum, but I know there is a product made for that purpose.  Does it darken enough to be considered 'black'?  Does it hold up well, or is fading an issue?  Anything else I need to consider?

Thanks for any advice.

Regards,
Terry


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## Flyinfool (Mar 16, 2021)

Anodizing is the most comon prosess to color aluminum. It is a durable finish. the color fastness is solely dependent on the dye that you use, some dyes fade really bad others seem to hold up pretty well. A quality paint will hold its color better than most color anodizing.


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## tjb (Mar 16, 2021)

Flyinfool said:


> Anodizing is the most comon prosess to color aluminum. It is a durable finish. the color fastness is solely dependent on the dye that you use, some dyes fade really bad others seem to hold up pretty well. A quality paint will hold its color better than most color anodizing.


Thanks.  Had not thought about anodizing, and I've never done it before.  I'll study that.  Any recommendations for products to use or others to avoid?

Regards


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## graham-xrf (Mar 16, 2021)

There are complete how-to's on YouTube.
Essentially you use diluted battery acid, although in theory, any electrolyte capable of working against aluminium can work.
You can practice using beer can ring pull tabs. Small DC wall-wart power supplies can be convenient, but if you have a electronics hobbyist power supply with current control, is better.

Aluminium is so extremely reactive that when fresh cut, it forms an oxide in fractions of a second. This layer is so thin it is completely transparent. Even quite thick layers remain transparent, until they crack up into white powder.. With both electrodes made of aluminium, connect the power will build up oxide on one side, and cut through the oxide and wear away the aluminuim on the other. You end up making a sulfate, and hydrogen I think).

Depending on the chemicals and currents used, you can make two classes of anodized coating. "Hard" anodizing, and "decorative" anodizing. The latter is quite tough anyway, and would be the type you dye. After the dye is on, there are processes to "seal" it.

There are just tons of YT videos on how to do this. Best advice - do not just go for the first one you see. Look at at least four. You will get an idea of the "better" ones quite quickly.

--> LINK


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## tjb (Mar 16, 2021)

graham-xrf said:


> There are complete how-to's on YouTube.
> Essentially you use diluted battery acid, although in theory, any electrolyte capable of working against aluminium can work.
> You can practice using beer can ring pull tabs. Small DC wall-wart power supplies can be convenient, but if you have a electronics hobbyist power supply with current control, is better.
> 
> ...


Thanks for the advice.  I just finished looking at two YT videos.  I'll need to do more studying, but my knee-jerk is anodizing is going to be exactly the finish I need for this part.

Thanks for answering.

Regards


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## Buffalo21 (Mar 16, 2021)

Wide tip Sharpie??....................


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## darkzero (Mar 16, 2021)

If you need it to be really black, anodize, cerakote, or paint.

For "blackening", there's a product by Birchwood Casey called Aluminum Black. Use it just as you would cold blue. But in my experience the stuff doesn't work that good, always gave me a dark gray instead of a deep black & it wears off easy. I don't recommend the stuff but you could give it a try, maybe you'll have better results than me? It's like $7 for a little 3 oz bottle.

As graham mentioned above about the different types of anodizing, standard "decorative" black anodizing will give you a glossy black. Black HAII & HAIII (hard anodized) will usually be a flat black. I'm not sure if anodizing types have evolved & are different these days.

I have no experience anodizing aluminum myself, only titanium, but when I was interested in DIY solutions it seem a bit dangerous & toxic to be doing in my home garage. Again, maybe things have changed these days? IIRC the hard anodizing can't easily been done at home. Also if you try to go to an anodizer, they'll have a minmum set up charge so it won't make sense cost wise if it's only a few parts or less.

Also check out https://caswellplating.com/ They have anodizing kits & may have their own aluminum blackening solution. Their products are great, never been disappointed in any of the stuff I have purchased from them.


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## tjb (Mar 16, 2021)

darkzero said:


> If you need it to be really black, anodize, cerakote, or paint.
> 
> For "blackening", there's a product by Birchwood Casey called Aluminum Black. Use it just as you would cold blue. But in my experience the stuff doesn't work that good, always gave me a dark gray instead of a deep black & it wears off easy. I don't recommend the stuff but you could give it a try, maybe you'll have better results than me? It's like $7 for a little 3 oz bottle.
> 
> ...


Thanks, Will.

I saw the Birchwood Casey product.  It's actually the reason I made the original post.  I've done a little bluing on steel with less than stellar results, so I'm not too confident I'll be satisfied with a similar product on aluminum.  Flat black is the look I'm after on this part, so I'll look into the Black Hall & Hall.

This will not be a high-maintenance application.  It will be a knob, so it will be handled some.  I'm a little concerned that paint may decompose over time.  Sounds like that may be an issue with Aluminum Black as well.  And the potential for gray instead of black is a definite deal breaker.  We'll see.

Regards


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## darkzero (Mar 16, 2021)

I've had good results with cold bluing steels with Caswell's stuff & Brownell's. But that Aluminum Black I could never get anything better than a dark gray. The Aluminum Black actually works better on brass, haha (same company has a blackener for brass too).

Even if Caswell has an aluminum blackener still I doubt it would hold up well on something like a knob that will be handled often.

Not sure if you are part of any gun or knife forums. Sometimes there are guys that offer cerakote services. Another option is powder coat. But like anodizing, there may be a minimum set up charge if you go to a professional service.


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## RJSakowski (Mar 16, 2021)

I tried the Birchwood Casey Aluminum Black and was not satisfied with the results.  It may be OK to touch up small scratches but fails a a general blackening.  Not much better than a sharpie and it rubs off.


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## tre_873 (Mar 16, 2021)

One of the Simple Green formulas is supposed to darken aluminum. Some of the pics I've seen look black. Not sure how long it lasts though.


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## darkzero (Mar 16, 2021)

The purple degreasers will darken aluminum also if used full strength & left on too long. Found this out by accident. It says on the bottle not to use on aluminum but hey, who reads labels? 

Still not a deep black, just a very dark gray like the alumnum blackener & its not very durable.


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## tjb (Mar 16, 2021)

Buffalo21 said:


> Wide tip Sharpie??....................


I use black and blue Sharpies on parts I'm milling to keep tabs on dimensions, hole location, etc.  Works great for that purpose, but usually after handling a few times, there's more on my hands than on the part.  For this application, it needs to be more permanent than that.


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## C-Bag (Mar 17, 2021)

Probably more involved than you want to get but nothing is as bulletproof as powder coat.


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## tjb (Mar 17, 2021)

C-Bag said:


> Probably more involved than you want to get but nothing is as bulletproof as powder coat.


Yep.  Best way for sure, but a little over the top for this application.  Paint is sounding better and better.


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## TIM-RANEY (Mar 17, 2021)

Just read a well-written article in "The Home Shop Machinist" (Jan/Feb 2021 issue) about anodizing aluminum without using a sulfuric acid solution. The process described uses sodium bisulfate (NaHSO4) available at pool supply stores. Various colors were achieved using RIT dye from the grocery store. He did not dye anything black, but the colors looked good. He used a 1 ampere battery charger for small parts and a 4 ampere charger for larger parts. With some experience with power supplies, various regulated DC supplies would work. And no, I have not done any aluminum anodizing. Just passing the info along.


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## Alter Machine (Mar 17, 2021)

As mentioned before there are 3 types of anodizing and 2 classes commonly. What's happening is the outer layer (we're talking .0001-.003) is being converted to an aluminum oxide crystalline structure. Most home anodizing solutions are decorative and provide good elemental resistance without surface distortion. Hard anodizing is a little more involved and require a means to control the solution temperature and a few other variables; it usually has a color phase from dull grey (thinnest layer) to gold to brown to black (thickest) and a somewhat flat or rough finish.

For your application powder coat is probably the more user friendly surface finish and with the introduction of polymer suspended ceramaics provide a durable hard finish with minimal dimensional change.


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## tjb (Mar 17, 2021)

Alter Machine said:


> As mentioned before there are 3 types of anodizing and 2 classes commonly. What's happening is the outer layer (we're talking .0001-.003) is being converted to an aluminum oxide crystalline structure. Most home anodizing solutions are decorative and provide good elemental resistance without surface distortion. Hard anodizing is a little more involved and require a means to control the solution temperature and a few other variables; it usually has a color phase from dull grey (thinnest layer) to gold to brown to black (thickest) and a somewhat flat or rough finish.
> 
> For your application powder coat is probably the more user friendly surface finish and with the introduction of polymer suspended ceramaics provide a durable hard finish with minimal dimensional change.


I tend to agree the optimal choice is powder coating.  Now it comes down to the issue of sufficiency: Is powder coating overkill?  Or, conversely, is paint inadequate?  I have a headache.


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## C-Bag (Mar 17, 2021)

tjb said:


> I tend to agree the optimal choice is powder coating.  Now it comes down to the issue of sufficiency: Is powder coating overkill?  Or, conversely, is paint inadequate?  I have a headache.


All these processes are not as simple as getting out the rattle can. I on average powder coat between 21 to 60 pieces a week so it works out for me, but it is a PIA because there are factors like the weather, humidity and wind that complicate whether I will even be able to do a run. But there’s no way I’d go through it for just one part.


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## 7milesup (Mar 17, 2021)

Eastwood https://www.eastwood.com/hotcoat-powder-coating.html has options.  
I have always wanted to try Cerakote https://www.cerakote.com/ but have not had a need yet. One application that you see it used on is firearms, which take a lot of handling obviously. Amazon even has it.... https://www.amazon.com/Cerakote/s?k=Cerakote


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## rwm (Mar 17, 2021)

Does anyone here have experience with Cerokote? It is just painted on or is it baked like powdercoat? How is it's durability?
Robert


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## Flyinfool (Mar 17, 2021)

Cerokote is not a product, it is a brand name. Just like there are a bunch of different kinds of Ford, there are a bunch of kinds of Cerokote with various properties, some are heat cure some are air cure. Best to go to their website to pick the one best suited for your application.
I have gotten away with baking parts in the kitchen oven on a day where the wife was not home.....


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## Bi11Hudson (Mar 17, 2021)

With my models, there is a large number of ZAMAK castings. ZAMAK is largely alum of course. I use Birchwood-Casey Alum Black prior to painting. Not so much a primer as a "backup" for scratches or flaking. The desired finish color is not a true black, but rather a variable very dark gray. By using the Birchwood-Casey product, a chip is virtually unnoticable.

*But*, and this does matter, the models are not "handled" on a serious basis. The "pre-blackening" is often used as a temporary coloring agent until I can get around to painting. It is *not* a true black and it doesn't stand up very well to handling. For something that would have constant handling, I would use a "Plasti-Dip" like product in the appropriate color. For handling as well as the electrical insulation properties.

Anodizing is not a solid option for several reasons, nor is powder coating. Setup time is a portion of this, as is the small quantities involved. In my case, very small details are inportant. Powder coating wouldn't work for that reason alone. I've never seen Plasti-Dip in black, but it should be available somewhere by someone.

.


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## COMachinist (Mar 26, 2021)

I have used Norrell molly resin that is a thermally cured phenolic coating specifically developed for ordnance usage on equipment and weapons. It‘s much better than any thing I have found to use on Aluminum that gets a lot of wear. Cerokote don’t even come close. My applications have stood up to some hard use for many years. No complaints at all.
check it out.
CH


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## hman (Mar 26, 2021)

Norrell's  | Norrell's
					






					molyresin.com
				



Looks like good stuff!


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## tjb (Mar 26, 2021)

COMachinist said:


> I have used Norrell molly resin that is a thermally cured phenolic coating specifically developed for ordnance usage on equipment and weapons. It‘s much better than any thing I have found to use on Aluminum that gets a lot of wear. Cerokote don’t even come close. My applications have stood up to some hard use for many years. No complaints at all.
> check it out.
> CH


Is it true black?


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