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)

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.

Lemon Method:
Time to get out the lemon juicer.

Cut four lemons in half, and juice them.
Take the juice, and put it through the finest strainer you have. The aim is to get rid of the pulpy stuff.
Make the amount up to about a cup by running water through the pulf then straining it. In this way you'll get even more 'lemon' from the lemon.

Now pour the lemon juice into a suitable container. Ideally this will be tall and thin, but still big enough to fit your part easily. Anything works, so long as your part fits into it.
Make sure your part will be completely covered. If if won't, then just add more water. No need to pulp more lemons, as the concentration isn't important. All that will happen is that the current will drop slightly.

Vinegar Method:
This is a lot easier that the lemon method, but it will use up vinegar, which you have to pay for. Vinegar also has a higher resistance, meaning the process will go slower.
For this you can simply pour it in (don't dilute it though). You can skip the next step as well, as vinegar is pure enough already.

Both:
There will be two electrodes inserted into this bath. One is the piece of work itself, which will be put onto the Anode. But you also have to have a Cathode.
For this take your scrap piece of Aluminium (one site recommends Lead, but I can't see any reason for it. If you know, please tell me), and attach the negative end of your power supply to it. It should be bigger than the part you want plated.

Mount your scrap somewhere within the bath, but make sure that the wire from the power supply isn't in the lemon juice. If it is then the wire will start to dissolve, and you'll end up copper-plating the piece you want to anodize.

Lemon is pretty gunky stuff, and even though you've strained it, you'll need to clean it of chemicals that will interfere with the process of Anodising. This doesn't take long.

Stick a piece of scrap aluminium in as the Anode (the other end, +ve, where your work will go later) and insert it into the bath. 
Once again make sure that the wire doesn't come into contact with the solution.

Run it for 5 or so minutes. You should see some bubbles form, and the colour might change.
  - If it goes green, then you've got some copper in there somehow.
Ideally it will look the same, but when you take out the Anode, you'll see some scum has built up on it. (As well as bubbles)

Take your scrap off the Anode, you're now ready to anodize your actual part.

Now we have a problem. We want to make sure that we only have Aluminium in the Lemon Juice, but we also want the whole part to be immersed, so it can Anodise properly.
The way I did it was by only inserting half the piece, and every ten minutes or so rotating it, so it ended up coating evenly enough.

Any part that touches the bottom or sides of the container also will not be anodized.

Run it. Let your piece sit in the bath for an hour or more.
- Bubbles will form. This is normal, and it is the formation of Oxygen gam at the Anode that makes the process work.
- Your solution may heat up as well. This isn't desirable as it will cause different speed plating, and so different size 'pores.' The only way I can see to offset this is to only run it for shorter periods at a time, and have a big container that will hold coolness for longer. I never noticed this as a problem, but if you are doing it commercially it might be.

If you remove the part from the bath and clean off the bubbles you will see that the object has gone matte. This is because the surface is now pitted with tiny little holes in a layer of the darker Aluminium oxide. When the layer is only thin, this can be scratched off with anything metal. When it is thicker it still can, you just don't notice it so much!

Finally remove the part from the bath, and rub it with some toilet paper to remove the lemon juice. 

The whole purpose of this was to colour the part, right?

One way to do this is to paint it. The heart was painted with acrylic paint, and while it could do with another coat, it's looking pretty good.

For the blue 'thing' I just dumped it in some blue/black Parkers quink, pulled it out, hung it from a thin piece of wire, and let it sit for an hour to soak in. I imagine that any ink or dye will work.
After it has soaked in rub the excess off with another piece of tissue paper.

You now have colour on your metal!


If you painted it, then you're finished, but if you dyed it, you may wish to seal it.

I haven't actually tried sealing yet, so I shall just quote some other places.

Leave the part in the boiling water or steamer for 30 minutes if sealant is used, and hour if it wasnt used.
 - http://www.engineeringhobbyist.com/projects/completed/anodizing/

Add color to your anodized metal by placing the metal into the dye solution. Heat to boiling and allow the metal to boil in the solution for about 30 minutes. Remove from the dye solution and rinse with boiling water, then set the dye by placing the metal into the vegetable steamer for about a half hour. Use tongs and gloves when moving the metal from station to station to protect your hands from the heat and from the acids you are working with.
- http://www.ehow.com/how_4491907_anodize-home.html
 

Wikipedia explains this whole water steaming part.
What happens is that it turns the metal into it's hydrated state, making it swell and seal in the dye. For some reason this doesn't stop the colour showing.

Next Steps:
Fist off, I''ll try sealing. Currently I don't have any reason to, but I may at some stage.

The coating on these parts wasn't very tough, it scratches off with anything metal.
Back at the beginning, wikipedia told me:
Harder, thicker films tend to be produced by more dilute solutions at lower temperatures with higher voltages and currents."
With the current gear at my disposal I can't create greater voltages. So it seems I'm stuck where I am.

Squeezing lemons is a pain in the neck. It takes ages, and is 'impure.' I may try other organic acids. Vinegar (concentrated somehow?)  seems the obvious one to try.