Colour change when clear anodising aluminum

A. Possibly there may be the following reasons
1. quality of the alum. alloys used. if iron or manganese quantity is high.
2. etching done at high temperature and may be high concentration of NaOH, subsequent bad rinsing water,
3.weak HNO3 Conc. in desmutting tank

A. Different alloys will produce different colors when anodized, depending on the alloying constituents. This is why "clear" is not really the preferred term. "Natural" is better wording. Generally, the purer the alloy, the more "clear" the coating. Of course, there are other variables to be considered, such as pretreatment, and coating thickness.

So basically, your anodizer is correct..in order to have your parts match in color, you should use the same alloy, and preferably from the same lot of material.

A. Stephen,

Adding to Marc's last comment......same alloy, same lot of material and SAME ANODIZER. There are too many anodizing conditions out there, with/without additives, different acid concentrations, different operating temperatures running at low / high current density anodizing...etc.

I agree

A. Hi Pradeep. Is the lighter shade a recent problem? Are you sure the anodizing thickness is the same as it used to be? The color saturation in dyed anodizing tends to be proportional to the thickness of the anodized layer.

But please don't frame questions in the abstract because then they can't be answered without a hundred ifs, ands, and buts :-)

Instead, please tell us who you are, what motivates the question, and what you know about the operating conditions. I don't really even understand what you are asking anyway. Is this oxalic acid anodizing, or clear anodizing with a chromic acid seal, or are you implying that you are doing two-step anodizing with an inorganic dye? Thanks!

Regards,