# How does color anodization work?



## Mags (Apr 30, 2006)

I am just curious. I actually dont know how normal anodization works either  but I figure that there has to be some difference.


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## metalhed (Apr 30, 2006)

Ok, I hope I get this right.

Anodizing is a process of surface-treating aluminum, by applying electric current to the individual parts while they sit in a chemical bath.

The current forces the aluminum to essentially corrode, or form oxides on the surface, in a controlled fashion. Higher current for longer periods produces heavier coatings of oxide on the aluminum.

Most lights, Mags for instance, are anodized with a relatively low level of current, and so have a fairly thin anodized layer. Sometimes colorings are added to the chemical bath, and this is how Mag makes their colored bodies (I believe.) Lights from companies like Surefire and Arc, are treated with higher current and so have thicker anodized layers, known as HAIII.

That's the short, non-expert answer. Take with appropriate levels of NaCl.


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## jsr (May 1, 2006)

As metalhed stated, anodization is a process of allowing the raw aluminum to form an oxide layer for protection. The oxide layer grows into the aluminum almost an equal amount to what is grown above the aluminum. Longer bath times do increase oxide thickness growth, but HCA (aka HA3) uses a different process requiring lower, very precisely controlled temperatures, as well as currents. The HCA process is more difficult due to the additional equipment required to drop and control the temp of the acid bath, so it's more costly. Color is added to the baths during anodizing and fills in some holes in the oxide to give the aluminum color.


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## David_Campen (May 1, 2006)

Here is my non-expert answer. Anodizing is an electrochemical process, as someone else said it is essentially forming a layer of corrosion on the surface of the aluminum, I think that it is perhaps aluminum hydroxide instead of oxide at first. To get colors dyes are added to the anodizing bath; dyes that bond to aluminum hydroxide are used. Finally the temperature of the process is raised to convert the aluminum hydroxide into aluminum oxide.


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## greenLED (May 1, 2006)

They add color to the baths? That doesn't sound right. I thought they dipped the freshly anodized parts into a dye bath before sealing the oxide pores. :thinking:

_Edit:_ I had to look it up to clarify the details:



> The anodic layer is also very porous as it comes out of the bath. Because of this porosity, it will absorb and hold dyes and colors well. The piece is usually colored simply by dipping it in a vat of concentrated dye for several minutes. Once the piece has been dyed, it is sealed, simply by immersing it in clean, boiling water for several more minutes.



Click here for the a simple description on how anodizing is done (with pics of the molecular structure, etc. In short: no, the dye is not added to the acid bath.


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## Dark_Shadow (May 11, 2006)

Yes, the coloring is performed after the anodic process. What is done is the part is put in a bath with DI water with mixed die and after that you seal the part in pure heated DI Water.

you can find a flow here:

http://www.focuser.com/atm/anodize/anodize99.html

I do work in this business so I know how anodize process work :naughty:


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## Flash_Gordon (May 11, 2006)

Here is a pretty good anodizing reference: Anodizing


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## tvodrd (May 11, 2006)

It ain't an acid bath, its essentially sodium hydroxide/lye. (Very high PH!) The color is added by a subsequent dye immersion. This is for both Type II and Type III. If they screw-up and don't immediately remove and rinse the parts after turning off the current, the bath will start removing the anodized layer!

Larry


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## MoonRise (May 11, 2006)

Umm, Larry, the actual anodizing part of the process is done in an acid bath. A common acid used is sulfuric acid. Other acids may be used as well, depending on the brew/recipe being used.

The sodium hydroxide bath is used in the process to clean/etch the workpiece(s) before the anodizing step.

You are right about the color being added in a dye bath step after the anodizing step and before the sealing step.


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## PEU (May 11, 2006)

yep the anno process is done in acid, the preparation stages uses alkalis and acids to remove any kind of dirt, then it goes to the annodizing bath at closely monitored low temperature, the temperature must be forced low due the increased current needed to "grow" the annodized layer on the ALU surface. Remember that the thicker the layer the more insulant it becomes

After the anno process, the longer the darker, the piece is dyed and sealed in hot water.

During the whole process the piece is kept in aluminium or titanium "hooks" that make electrical contact with the pieces.


Pablo


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