Natural anodising

Hi - I've searched the forum and found good stuff on anodising but have not found an answer to my specific question.

I plan to have a go at home anodising if I can get some battery acid and using aluminium kitchen foil as a cathode, a battery charger as a power supply and aluminium MIG welding wire to connect the power supply positive to the component. I do not want to dye the component, so my question is - can I just miss out the dyeing stage and go straight from the electrolyte bowl, via a cold water rinse, to the boiling water sealing pan?

Thanks in anticipation and season's greetings!

Hi Otley,

no need to dye the component, your method should work. I have anodized without using any dye and it worked.

Thor

The dye is an addition to the basic process. So yes you can do exactly as you describe with no problems.

cheers

Bill

Thanks for the replies - I'll give it a go. I managed to get some acid from a local battery stockist. £3.60 for 2 litres. Car accessory shops aren't allowed to stock it anymore, apparently.

The main thing Bill, is cleanliness and chemical cleaning. You obviously know that you have to etch the Alu. with a caustic solution? You should also see if you can get some , 'Anti smut' solution and you use this between baths.

Finishing is with a Lanolin solution which fills the pores of the anodising. Make sure you leave no salts in any holes as corrosion will occur. A boiling water bath will suffice.

As an aside, we have a powder coat plant next door to us at work and I have been watching, they pre-heat the item and then spray the powder and according to the chap it saves using static attraction. The finished items look as good as any I have seen.

Clive

I thought the caustic etch was to produce a matt or satin finish. I was planning to scrub the item with soap and water prior to the anodising bath. Will this not work?

What is the lanolin solution that is used in place of dye? Are you saying that going straight from anodising bath to seal pan will result in porous anodising if I don't use this lanolin?

The lanolin is to seal the pores caused by the etch! There are other proprietry solutions on the market that seal the surface. The etch bath prepares the surface for the actual anodising function. By all means clean as you have described but the surface finish is only as good as the etch depth and that is a function of time in the etch!

The etch takes materiel off and the anodising puts some back on and makes a durable surface. At that point you put it in a colour dye or leave natural colour. Then you seal the surface. Durability is graded as a number and 25 being used for outdoor exposure and cosmetic as number 5. Remember that most anodising is done in large batches for uniformity of surface and colour so that a rigid time sequence is required. It is not just a dip and dunk system.

Clive

I thought you could do the sealing by boiling in clean water?

Neil

I've done quite a bit of anodising, and I used to do the acid etch and de-smut, but now I've simplified and still get good and consistent results.

That battery acid needs diluting with the same quantity of distilled or de-ionised water, and remember to AlwaysAddAcid, never add the water.

Polish the part you want to anodised, then scrub it in hot soapy water. Wear surgical gloves or you leave fingerprints. Rinse well in cold distilled etc, you can buy it in 25litre drums at my local battery depot for £10. Suspend in the acid from aluminium wire, with positive connected to the part (which then becomes the Anode), and the negative connected to a large piece of lead sheet submerged in the acid. Length of time depends on size/current available, but after time is up, lift it out of acid (gloves&goggles) and into rinse water. Drop it into boiling water for about twenty minutes, although I use a pressure cooker. After boiling let it cool, but whilst it is still quite hot, rub it all over with a candle, thenbuff it with a soft cloth. Job done.

Since my original post, I've had a go and found it surprisingly straightforward. I used two pieces of lead flashing for the cathode, placed at each end of my plastic tank. I found a recommended current density of .012 amp per square cm for an hour. I constructed a spread sheet to allow me to quite precisely calculate the surface area of the components and ended up buying a current limiting 30V, 5A lab power supply off ebay so that I could set the required current.

What surprised me was how effectively anodising makes the surface non conducting. If you want to test a piece of alloy to see if it is anodised, just touch the probes of an ohm meter to its surface. Anodising will stop the meter beeping. If it's anodised, dip the item in caustic soda for a few seconds to remove the oxide layer and it will then conduct.