Originally published at: https://boingboing.net/2020/10/29/anodized-titanium-turns-different-colors-based-on-voltage.html
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Titanium anodizing color is based on oxide layer thickness (soap bubble effect), which correlates to the voltage it can insulate against. Up the voltage and the oxide layer will thicken until it again can insulate against the higher voltage. You can do a lot of different colors, but not red.
Aluminum anodized color is either clear or brown/black depending on the milspec and alloy grade. Any other color is due to dyes. The initial anodizing creates a pitted oxide surface, the part is soaked in dye to fill the pits, then a nickel acetate or boiling water rinse is used to seal the pits and trap the dye.
I actually have a patent using titanium anodizing. It’s fun using a voltage supply and diet coke to demo anodizing scrap titanium.
And I had a hospital call about a product line our company acquired asking if it contained any nickel (nickel allergies can be serious stuff). The patient was literally on the table ready to be cut when they called. I was in the process of switching the line from nickel acetate to boiling water, so told them to NOT use our product.
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I make chain mail out of titanium rings that have been colored this way. You have to be sure to order all your rings at once to make sure they’re all mostly the same color, as the next batch of “blue” or whatever won’t necessarily be the same shade.
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You are 100% correct.
Titanium annodizing for color is done solely without dyes- using only electricity. Aluminum anodizing is usually done with dyes for color in addition to using electricity.
I don’t know a ton about titanium annodizing (though I know a ton about forging titanium, used to make the tooling for that), I do know a fair bit about aluminum annodizing.
If you guys really want to have your minds completely blown- once you realize anodizing is just a porous oxide layer to aluminum, kind of like crust on bread, you realize you can fill it with not just die but other compounds.
It is possible to get aluminum anodized with Teflon impregnation in the pores- so you get something that’s a hard surface coating and a color, but is also functionally very slippery!
This is a special option that my local anodizer offers.
There are actually several different types of anodizing with aluminum and titanium. I can only speak for aluminum grades, since the product I helped design we ended up having anodized so I had to research.
Standard type 2 Anodizing is what people normally think of and is normally a color and it’s a very very light oxide layer it’s mainly used for coloring.
Type 3 is called hard coat anodizing- and they apply more current through the aluminum and it creates a much thicker layer of the oxide that they do not dye- and it creates an extremely tough surface on the object.
Gun parts usually get this kind of treatment. It’s normally dark grey in color.
There is a special type of anodizing that instead of using typically organic based dyes for the color, metallic based compounds fill the pores. This is a special subset hard to find often called architectural annodizing. Because the compounds that provide the color directly come from metal ions they do not break down in UV in sunlight so they are very colorfast for outdoor applications or aluminum artwork.
I’ll throw this out there for people wanting straight jet black aluminum- Birchwood Casey makes a chemical system called Black Lumiclad that you can do at home with a bunch of 5 gallon buckets and it produces a very good wear coating and the deepest black you will ever see on aluminum, but it is also resistant to heat. I was looking at blacking out my motorcycle engine since it is solid cast aluminum and anodizing is expensive and changes tolerances of fit, and every paint I tried flakes off including high temperature powder coat.
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I always learn so much on the BBS!
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I played with anodizing aluminum a bit in my jewelrymaking classes. One of the assignments was to make an ornamental piece of tableware. I made a knife blade from scrap aluminum, then anodized it 2 different colors; the handle was a piece of antler I had socked away.
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Does it affect titanium or aluminium in any other way if anodised? What if I have a bike frame, e.g.? Possible, at that size? And: affecting stability?
I bought earrings from a street artist in SF ~1982 and she explained this process. It was all the rage by 1985. Maybe old is new again?
Coolest thing I’ve seen is miniature paintings done by anodizing titanium.
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I once read an article about painting anodised colours on metal - the paintbrush had a current running through it, and made a circuit with the metal that was being painted. The cool bit was that a foot-pedal was used to control the voltage and thus the colour. Very neat.
Link? This seems really cool!
Technically, yes. You are converting some of the metal to oxide. Your hypothetical bike frame would be weaker. The titanium anodization can be measured in nanometers, the aluminum could be thousandths of an inch. But those are pretty thin, so for practical purposes, you haven’t hurt the part.
Anodization, if done correctly (which is why there are specifications), makes the parts more stable. Aluminum oxide is the same chemical compound as sapphire. That makes for a wonderful protective coating against abrasion and corrosion. Not perfect, but pretty good.
One other thing: aluminum parts get appreciably larger, so critical fitting parts might not fit if the anodization isn’t factored in ahead of time.
Since we’re talking protective metal coatings, there’s something like anodizing done to stainless steel called passivation. You soak the part in nitric or citric acid to eat away all the iron on the surface leaving only chromium on the surface. The chromium oxidizes to form a clear protective barrier. No iron + clear coating = minimal chance of rusting. Remember, it’s called stainless not stainfree.
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