Chemistry question regarding anodising Aluminium

[SeaMonkey]

Please do!

 

I'd love to see how it turned out.

[stix]

Please do!

 

I'd love to see how it turned out.

.

Cheers SeaMonkey. Ok here is the result:

 

The piece on the left is the new black version, the piece on the right is the original black.

 

With the lighting in the photo, its' hard to show it exactly, but it's pretty close to what it looks like. The original old black is more rich than the new one. Nevertheless, the new one is way way better than I was getting in post #47. Why??

 

Well, I think this is what happened. The other day (prior to post #48), just by chance, I happened to notice that there were crystals forming on the bottom of the anodizing tank. Maybe it was always on the edge of supersaturation, but this time I actually noticed it. In Melbourne Australia, we are in the middle of Winter. Around 8degC at night to maybe 13 during the day (46-59F).

 

After noticing the layer of crystals - probably around 2mm (1/16th") thick, I stirred up the solution with a stick to dissolve the crystals back into the solution. With limited success. So I went out and purchased an immersible aquarium heater. I set it to ambient temperature (21C/70F), gave it a mix around and the crystals dissolved back into the solution.

 

So I went forward with the "new black" anodizing process. It takes around 2hrs in the bath. At this point I was getting quite hungry and since it was getting close to tea time I decided to start making a nice vegetarian lasagne. I had already rinsed and soaked the lentils overnight in the refrigerator, and as I was sweating off the onions - you know, when they get to that "translucent" stage and just starting to stick to the bottom of the pan, just becoming caremelized... although, I'm not sure if that part is relevant.

 

Regardless, I got to thinking about the main anodizing Black issue I was having. Well, from most YouTube vids I've seen, most people are using Sulphuric Acid as the electrolyte. There is a real issue of over-heating that can occur during the anodizing process and could possibly get out of control and this concerned me. Some people introduce an internal refrigeration system in the bath/tank to cool it down. For small operations like mine, you can immerse a bottle or two of frozen water to get the temp back under.

 

Well, I'm not using Sulphuric Acid!! I'm using Sodium Bisulphate!! I imagine that Sulphuric Acid doesn't crystalize easily at low temperatures otherwise car batteries wouldn't work?? I was always checking the temp thinking that it may increase at any time. It never did. Quite the opposite it seems.

 

I'll just point out again that during the last 7 weeks or so, I have NEVER had an issue when using the correct aluminium dyes (red and blue) it was always the black clothing dye. Therefore, it seems to me that the proper dyes have a lot of tolerance when it comes to temperature of the solution. The thing with the clothing RIT dye is that according to instructions, you use it with water just under boiling.

 

When sealing the Aluminium after the dye process - to keep the dye embedded, you immerse the piece in just off boiling water to close the pores of the aluminium oxide layer. This is the same temperature that the RIT dye works best (with cloth). Not that I ever did, because you would be trying to dye the piece at the same temperature as sealing it . The proper Caswell dyes work best at 60C for good reason.

 

What to do now? Well, I don't need a lot of black pieces for my prototype, so I could just continue with the RIT dye for an inconsistent black. BUT now it's really p*ssing me off! and due to my "Obsessive Compulsive Disorder", I simply MUST now purchase the proper black dye, which I was trying to avoid in the first place, just to prove a point!... I don't really want to... Do I? It's cost me way more in the end. Not just financially, but mentally.

 

FWIW, this is part of my anodizing setup. 15Litre bath.

 

 

And it continues . . . . . .

Edited July 16, 2021 by stix

[stix]

Like I said previously, I can be a tight-arse. Not necessarily because of money. I don't like that qweezy feeling of thinking you are being ripped off. I actually rang up Caswell Australia yesterday to inquire why the black dye is more than double the price of the beautiful colours. Maybe they made a mistake with the pricing on the website? I was told that the chemistry for black dye costs lots more to produce. Ok, fair enough. I'm still not convinced.

 

Like, when my colour printer ran out of... colour... I went to my local stationery shop to buy new cartridges. The cost of the replacement cartridges where just slightly less than buying a whole new printer. I'm sure lots of us have been there.

 

But, out of sheer rage and "bloody-minded-ness" I bought the cartridges. When I got home and relaxed and thought about the whole thing... I made a stupid decision based on emotions than logic. That's sort of how I feel about the black dye. Like being forced into something to be ripped off, but sort of not smart enough to realize that you gonna get ripped off anyway.

 

Greedy Pigs:

https://soundcloud.com/user-566434468/fat-cats-greedy-pigs-vst-mix2

[stix]

I've ordered some "Caswell" black.

 

I could have driven my car to pick it up, but we are currently under a 5km radius curfew (lockdown).

 

Hopefully it will arrive in the next couple of days, and then I can continue my aimless experiments. Afterall, what the f*ck else do I have to do?

 

[robbo]

Of course sweating the onions and getting them caramelized is relevant! Otherwise, why bother with onions?

[stix]

Of course sweating the onions and getting them caramelized is relevant! Otherwise, why bother with onions?

Ha Haaaa

[stix]

The "Caswell" dye is the way to go. I'll post images of the "real" black black, if anyone is interested.

 

As an aside, when I was sanding down an old anodized piece, I got "sparks".... sparks... sparks?

 

Only on the anodized surface - it really freaked me out.

 

Why?

[justvisiting]

The anodic film is made of aluminum oxide, which is commonly used as an abrasive on sandpaper. It's what rubies are made of. Cutting anodized aluminum will generate sparks, and it dulls the saw blades pretty quickly in a factory situation. I have never heard of using sandpaper to remove anodizing.

 

Removing the anodic film for re-processing is commonly done with a hot solution of caustic soda, which is also used to create a matte finish by etching prior to anodizing. It's preferable for the etch/ strip solution to have a fairly high amount of dissolved aluminum in it to tone down the aggressiveness of the attack on the metal.

[stix]

The anodic film is made of aluminum oxide, which is commonly used as an abrasive on sandpaper. It's what rubies are made of. Cutting anodized aluminum will generate sparks, and it dulls the saw blades pretty quickly in a factory situation. I have never heard of using sandpaper to remove anodizing.

 

Removing the anodic film for re-processing is commonly done with a hot solution of caustic soda, which is also used to create a matte finish by etching prior to anodizing. It's preferable for the etch/ strip solution to have a fairly high amount of dissolved aluminum in it to tone down the aggressiveness of the attack on the metal.

I was using as disc sander - just mucking around. I was surprised to see sparks.

Sodium hydroxide (caustic soda), is the last step I do, the final clean, before anodizing.

I was surprised to see sparks!!!.

As you say, anodizing can be removed via a soak in NaOH. I just wasn't expecting sparks.

[stix]

As per post #53 & #54... etc... - I've got the "Caswell", dye.

 

 

Not the best image, but it is clear to see (in my view) that one of them has a much more rich black.

 

Cost me a "pretty penny" just to prove a point . But the point is proved beyond doubt.

 

So, in the end it was not the chemicals, ie. the electrolyte solution. It was the Dye that caused me many issues and sleepless nights. A long and expensive path of investigation.

 

At this point, using Sodium Bisulphate to anodize aluminium is a bloody great alternative to Sulphuric Acid. Just don't skimp on the Dye.

 

https://soundcloud.com/user-566434468/fading-away-vox-ideas

[SeaMonkey]

Fantastic!

 

That is what the "Scientific Method" is all about!

 

You've done us all a great favor by your line of experimentation.

 

Proving, once again, "Where there is a will, there is a way!"

[stix]

Thanks man.

 

I thought I may as well post this image, the last one, to prove a point.

 

 

The RIT dye is not as rich black as the proper Caswell dye, and not as predictable.

Nice Red and Blue... ooohhhhh... Shiny!!!

[justvisiting]

It would have never occurred to me that sodium bisulfate would be a good electrolyte for anodizing. Beautiful finish on those parts!

 

The most beautiful black I've ever seen on an anodized object is the gloss black on a Maglite flashlight. I don't know how they did it, but I was never able to produce such a perfect finish in our plant.

 

The most interesting thing I was ever asked to anodize was the inside of a fuel tank for a drag racer. To validate the success of the interior anodizing, I colored it with an inorganic gold, based on ferric ammonium oxalate. The dye was called Aluminum Fast Gold L, from Clariant (formerly Sandoz).

[stix]

What i've learned is when anodizing aluminium, the underlying finish shows though in the final product.

 

The best "Maglite" type shiny finish i've got so far is:

 

 

It was the first test I did with the Caswell dye. It was shined up a bit.

 

In post #62, you can see the "brushed" and semi-gloss look, which is what I wanted. I used coarse sandpaper over a spinning mandrel on a bench drill, then immersed in sodium hydroxide for the final clean. A brushed semi-gloss finish.

 

For a more "shiny deep black", I would use fine sandpaper, then finer sandpaper, then finish up using fine grit car polish. When done, the finish is almost as good as chrome. Then you anodize it. Skip the sodium hydroxide, just make sure to clean it well first.

 

Although I'm making "jigs" and other pieces - to make my final product, I could be persuaded to show how that "Shiny Maglite Black".... I think...

[stix]

A new kind of Shine?

https://soundcloud.com/user-566434468/a-new-kind-of-shine-final-more-bass

[justvisiting]

The Stixstudios pic is pure gold! The rodeo song was fun too 'I am a spleena' has what us North Americans might call an Australian sound to it. What's a spleena, BTW?

 

I'd like to see a Maglite shine done at home, if you can.

[stix]

A "Spleena" doesn't have to prove him/her self.

There is no requirement to be a "spleena", just self actualization - it's easy.

 

Us Australians are pretty cool, and best to help others.

 

Some people hold their knowledge to the grim death end. That is so f*cked. Share what you have learned!! It is a way better way to go.

 

Are you a Spleena?

https://soundcloud.com/user-566434468/fading-away-vox-ideas

 

I will do my best to show how the "Maglite Black Shine" is done at home.

[stix]

Other things to do.

 

I'd be happy if someone told/showed me a technique - how to bend aluminium. That would be cool.

[stix]

https://soundcloud.com/user-566434468/test-tune4