Step 6 Prepare the aluminium for treatment
With the tank constructed the next step is to prepare the aluminium for treatment. If the components are in a clean, non-corroded condition then they can be anodised without any pre-treatment - if not, then a caustic solution of Sodium Hydroxide (drain cleaner) at about 15% WW can be used as a dip to brighten the metal.
# Important note: keep the acid and alkali baths well seperated.
Step 7 Handy tip
During anodising it is normal to see small bubbles forming on the work-piece, but if any large bubbles form in one spot there is a chance that they will effect the final finish. It may be necessary to stir the solution occasionally or, especially in the case of concave shapes, you could use an aquarium air-pump to continually agitate the acid bath. The wire I've used to suspend components is 0.8mm shaved aluminium MIG welding "rod"...ferrous wire is a definite "not".
Step 8 Its all in the timing
The time it takes to anodise a piece depends on several factors including its size, the amperage of the power supply and the required thickness of the oxide layer-the thicker the layer the more durable the finish and the more dense the final colour. The layer of anodising is measured in microns, and to get a very deep colour, especially "absolute black", will require a layer of at least 12 to 15 microns. This is one of the benefits of anodising-you get colour without the surface build-up of paint.
Step 9 Developing electrical resistance
When the oxide chrystallises it develops a progressively higher resistance to electrical current, as the anodised surface is a layer of aluminium oxide rather than actual metal. By placing a multi-meter into the circuit you will be able to see the current drop as it occurs. The main point is to ensure a good electrical connection is maintained right throughout the anodising process.
Step 10 Water gets rid of any residual acid
Once the part has been anodised, it needs to be thoroughly flushed to remove all residual acid. At this stage of the process the oxide layer is porous, at a molecular level, so soak it for a few minutes in demineralised water, so the acid is dispersed from the chrystalline structure. Demineralised water is the suggested medium, so thats what I used at first, but when it ran out I found that tap water works just as well.
Step 11 Parts take on a milky grey colour during anodisation
You will notice that during the electro-chemical process the anodising part will take on a milky grey appearance as the oxide layer is forming. This look will become even more evident afterwards, when the part has been washed and dried. As mentioned, the anodised layer is very porous at this point, so don't handle it with your bare fingers as this will result in there being "stains" in the final finish.
Step 12 When it comes to dyeing: alfoil bad, plastic good
Time to dye!!!
There are several different products that can be used to colour anodised parts-vegetable based dyes, diluted writing inks, histological dyes and commercial anodising dyes; the latter being used here. The dyes come in powder form and are mixed with demineralised water. To ensure maximum penetration into the chrystalline layer they should be kept at a temperature of 80 Deg C. A word of warning, when left overnight they eat through alfoil containers...use plastic!!!
Step 13 Appearances are deceiving-green turns out gold
The colour of the solution can differ markedly from the finished product-green actually turns out gold!!! The solution is a true dye, that is, it changes the colour of the actual metal, and therefore it takes a few minutes for the pigment to penetrate the actual oxide layer-which at this point has a "sponge" like porosity. The longer the part is left in the dye the darker the finish, so if you are anodising several parts it is tricky to get an exact match unless you use a stopwatch.
Step 14 Boil or steam the part till its well done
After you have achieved the colour that you want, the next step is to either boil or steam the part for around 20 mins. If the colour washes off then something has gone seriously wrong-such as a lost electrical connection has occurred part way through the anodising process. Boiling converts the oxide into a different chrystalline chemical form, sealing the porous layer and permanently trapping the dye underneath, below the surface of the metal.
Step 15 Polishing with a cloth reveals a deep lustre
After sealing, the part will air-dry to a matt finish that looks fairly ordinary. Fear not, this is just the residual dye left on the surface, and polishing it over with a cloth will reveal the deep lustre that you were hoping for. Additional shine can be achieved by using a soft abrasive-car polish is perfect-to remove any small imperfections and add some "reflective" properties to the oxide surface. Anodising won't chip, peel or scratch easily, making it one of the most durable finishes you can get.
Some ideas for anodising could be a 5.25in faceplate from a Nexus Superpanel, which only shipped in silver. Checker plate and expanded metal are some others that rate a mention, and would look cool for a case mod, but ultimately its up to you. Not too long after you have finished admiring your handiwork, you will realise that you are now left with an ecological issue-getting rid of the toxic chemicals all over your workshop. Disposing of the Sodium Hydroxide is a cinch...its made for cleaning drains, so thats the best way of getting your money's worth. Just make sure to follow the instructions on the bottle. The dyes are non-toxic, so they can be poured down the drain with plenty of water, or into a hole in the garden to disperse over time. The big issue is the sulphuric acid. It is nasty, toxic and dangerous to have hanging around the house, and shouldn't go down the drain either :shock: . The answer is to return it to the place of purchase, or dispose of it responsibly.
# HOT TIP: Wear safety equipment and slowly pour the acid into a container of anhydrous lime, it will turn into a neutralised paste. Let the pate dry off to a "play dough" onsistency, wrap it in newspaper and put it in a garbage bag. It can then be disposed of through the normal refuse system. So, be planet friendly.
Here are some other ideas if you are keen, and a demonstration of the colours available
Have fun and above all...enjoy-PV