Color on Anodizing

Anodizing is an electrochemical process that thickens and toughens the naturally occurring protective oxide. It's an electrochemical process where the aluminum on the surface is converted to aluminum oxide. Due to its permeable nature, sulfuric acid anodizing is excellent for color dyeing and provides a base for primers, bonding agents and organic coatings. Sulfuric anodizing provides corrosion resistance and is very durable. The result of normal sulfuric anodizing is a thin coating of aluminum oxide on the surface of the original aluminum The freshly anodized part is immersed in a liquid solution that contains dissolved dye. The porous anodic coating absorbs the dye. The intensity of color is related to the thickness of the anodic film, the dye concentration, immersion time and temperature, among other things. There are numerous sources for obtaining colour dyes. You may refer US source http://www.reliantaluminumproducts.com.

Aluminium anodizing is a two-part process. The first step is the artificial growing of a relatively thick oxide-layer in sulfuric acid. After this first step the surface is still open, porous on a micro-level, allowing for the application of almost any dye consisting of small enough particles to enter the porosity. First rinse the surface very thoroughly with a low pressure jet of lukewarm water to remove any remaining acid and dry it with warm (not hot) air. Avoid touching the surface as much as possible, at least with hard objects. Next I used to make drawings/paintings with solvent-based felt-markers in any available color. Finally the surface has to be sealed, which is usually done by immersion in hot steam (at least 140ºC) for 10-30 minutes. The dye will be sealed inside the oxide layer, but exposure to UV-light will still affect it. For long lasting outdoor use I'd recommend industrial dying stuff (I used to use Sandoz' Sanodal), although some colours will still faint or bleach in time. You can also apply any dye through silkscreen printing, e.g. to tranfer photographic images. Great possibilities for artistic applications, but rarely employed.