Anodizing Metal at Home (The LJS method)

In my free (pah, free) time I do metalworking. Sometimes I make Mini Swords, other times Jewellery. Sometimes I make things that even I don't know what to do with them.
But regardless, they are all silver and shiny.

Seeing as a lot of my recent jewellery has been made from Aluminium, I decided to look at Anodising. After Anodising Aluminium it should be more receptive to paints and dyes.

This instructable will cover the process of Anodising and Dying small Aluminium parts using materials that anyone can find.


Oh, and LJS? Lemon Juice Substitution. I use it as a generic electrolyte for any electrochemical reaction at home.


The Setup:
Small container. Mayonnaise container, jam jar etc.
Aluminium scrap
19V+ power supply going to crocodile clips (May work down to ~12V. Read the next page)
Coke can
Patience

Consumables:
4 Lemons (Or lots of vinegar)
Water
Object to be Anodized (Aluminium)
Dye, ink or paint (I used Parker's Quink, but you can use just about anything though)

Step 1: The Theory

I had heard about Anodizing before, and seen it often enough, so it was natural that when I wanted to colour metal, it would come into my head.
My first step was to gather information. As per my usual on the web, it was Wikipedia first.

Here are the claimed benefits of Anodizing:

"Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than does bare metal. Anodic films can also be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add interference effects to reflected light."
Anodizing - Wikipedia

After wading through the first paragraph or two, I came across good information on the process. It goes something like this:
1) Clean it
2) Put it in an acidic electrolyte.
3) Run a DC voltage through it.
4) Dye/paint it.
5) Seal it

Of course there is a little more involved. I'll go over these in depth in later steps, but here's the overview:
They recommend cleaning it in a solvent bath. I rubbed it with methylated spirits.
They suggest using ... Sulphuric acid. I don't have any, nor do I want any. However, lemon juice is acidic and conducts well enough.
Apparently the process can take anywhere from 1-300 volts, but Wikipedia adds:

"most fall in the range of 15 to 21 V"
Anodizing - Wikipedia

It adds a final piece of advice for us home experimenters:

"Conditions such as electrolyte concentration, acidity, solution temperature, and current must be controlled to allow the formation of a consistent oxide layer. Harder, thicker films tend to be produced by more dilute solutions at lower temperatures with higher voltages and currents."
Anodizing - Wikipedia

Now it was time to go and see just how well it would work.

Comments

[jaggdlynx]

Would it be possible to wrap bare copper wire around the inside of the glass jar to use as the anode? I've seen it done on a larger scale in 5 gallon buckets, but he was using industrial chemicals and it wasn't quite the "can do at home" type of set up. I only ask because I see you mention if the lemon juice turns green it means you have some copper in there somewhere, so I am guessing it's not a god idea with this particular set up (?).

[sdfgeoff]

Actually, it will be fine using copper for the cathode. Just make sure that you don't end up copper plating the part (check the polarity of the wires).

[Lectric Wizard]

Try pickleing vinegar it is much stronger than regular table vinegar, might help...

[audreyobscura]

I would love to see posts about your experimentation with other organic acids.

[sdfgeoff]

I'll let you know whit I've tried.
I've just added Vinegar to the ible, and plan to try orange juice and some other stuff sometime soon.