Anodising is the process of anodic oxidising where a oxidic protective layer on the aluminium is produced.  THis process does not actually apply a protective layer on the material but creates a thin oxide layer by converting the top metal layer.  The aluminium is anodised by immersing it in an acid (the electrolyte) and applying Direct Current (DC) electricity, with the work-piece positively charged. The electricity splits some of the water in the acid,  into positively charged hydrogen (H+) and negatively charged oxygen (O-), where it reacts with the aluminium to form aluminium hydroxide and related compounds. It is important here to remember the dual nature of the acid;- whilst it helps to conduct the electricity; it also attacks the anodized film at the same time. The acid helps with forming the anodic structure and at the same time anodising poreworks to dissolve it.

This is not necessarily a bad thing. Rather, the simultaneous formation and dissolving of the anodized film creates a coating that has a porosity in the form of microscopic "drill holes" extending from the surface almost to the raw aluminium.

In colour anodising, the pores in the thus created coating absorbs the dye, and then the coating is "sealed", locking the dye in. The strength of the colour will depend on how thick the coating produced during the anodising precess is, and thus how much dye it can absorb. So light pastel colours can be obtained with a minimal anodising thickness.  to get a fully saturated dark black (jet-black) colour may require a greater thickness. All of our dyes used in anodising aluminium are industrial strenght specialised organic dyes, with good colour-fastness and are the same as those being used by commercial anodising companies.

Whilst we have heard of DIY users using simple dyes such as food, leather and textile dyes these are not suitable as those have no resistance to sunlight.  I certainly don't understand why one would go to the expense and trouble of making a beautiful crafted aluminium article only to then dye it with an inferior dye.  

Personal Safety is Important

goggles-gloves-overallPersonal safety equipment such as goggles, gloves as well as splash gown must be used all the time during all operations in the anodising process.  When handling acids, it is prefrable to use a full-face face-mask  but at least wear safety goggles to protect the eye. Gloves need to be used for hand protection. Also ensure that there is good ventilation to safeguard your breathing system.   Adequate personal protection is strongly advisable!

Colour Anodising Sequences

The anodising process is not completed in a single anodising tank but includes a number of pre-treatment steps before the anodising occurs and has a number of post-treatments after it.

The most common sequence, would be the seven steps:-

          1. Clean
          2. Etch
          3. De-smut
          4. Anodise
          5. Neutralise
          6. Dye
          7. Seal

each with a rinse after the process as in the diagram below

               anodising process

               

Depending on the  grade of aluminium used, not all steps may be necessary.

If a matt finish is required, the alkaline etch process does produce a matt finish on the anodized parts. The longer the treatment time, the deeper the etch and coarser the surface obtained. Similarly , a chemical or electro-polishing process can be used to brighten up the parts prior to anodising.

Safety

It is VERY important  to ensure that you allways keep childeren away from this process, as you are working with corrosive liquids; and considder carefully when you are storing the various items that they are kept in a secure and safe location


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