Looking for information on anodizing

A. Peter:

It sounds like you are describing two-step anodizing. The first step is a conventional sulfuric anodize, and the second is an anodize bath containing a lithium salt. The lithium deposits into the pores of the coating. the longer you anodize in the second bath, the deeper the color becomes. Unfortunately, all my reference books are at work...

A. Peter,

The process you described sounds like titanium anodizing. It is true that the color is controlled by changing voltage for anodizing Ti in phosphate solution.

If you want to anodize aluminum alloys with different colors, however, it is a different story. In this case, you may refer to the information in Gerald's email.

Ling

A. Hi Peter. Please search our site for "color anodizing of aluminum". As Ling says, the colors of aluminum anodizing are from dyes absorbed into the pore structure, not from thin diffraction films as in titanium anodizing. The usual process solution is 10-12% sulfuric acid by volume, and the usual voltage is about 12 volts, with a current density of perhaps 12 ASF. After anodizing to a thickness of .0002" to about .0008", depending on how dark and saturated the color must be, you dip it in dye, then close off the pores by swelling the aluminum oxide in steam, hot water, or other sealants.

Best of luck.

Regards,