View Full Version : Anodizing question

05-08-2003, 12:19 AM
Okay I have heard two stories over the years about how the colors are achieved in anodizing,one is that a thin coat of aluminum oxide is built up and then the part is dyed and sealed with more oxide,and that something like the current involved is changed.I suppose that both are posible but which is it?Seem like I remember that several jem stones are actually aluminum oxide,but differnet conditions allow different colors,anybody know?

05-08-2003, 12:24 AM
According to my books.. it is the dye in the surface and just under it in phosphates created by the electrolic action. The surface is harder than just the aluminum. but.. it does fade. You can anodize with muratic acid and a battery charger. all available to US hsm's

05-08-2003, 12:30 AM
The colour in hard anodising is a clear layer of Aluminum Oxide - which naturally occurs over time with raw Aluminum anyway. After the Aluminum has oxidized it is pretty well chemically inert.

Hard Anodizing first dyes the porous surface and then seals it with a layer of Aluminum Oxide. This gives a very hard surface with a lower coeeffecient of friction (great for sliding plastic over).

The dyes in certain colours can be very expensive - black is cheapest, red most expensive. Dyes used for clothing have been known to work.

It is possible the analine dyes used by wood workers could work very well (I am speculating here, I have not tested this myself) - if they do they would provide a wider brighter spectrum of color.

05-08-2003, 01:31 AM
Dyeing is done after it is anodized and before it is sealed. The sealing process is nothing more than dipping in boiling water. This is why temperatures are critical in the actual anodizing process. Also, there are many different anodizing specifications, but this is the easiest and most common for the "home shop".
No conection, but a good site that details the procedure is: