Why does Anodized Aluminum Vary in Color?

In my experience with anodizing any of our aluminum products, I have learned that the words “variation” and “shade” go with the territory. Unlike factory paint, which is a color specific finish, Color Anodizing is a difficult and varied aspect of our trim business. When a particular paint is specified, the architect issues a manufacturer name and product number which is then pulled and duplicated by any factory paint facility. If a paint number is not provided, then a color swatch or sample can be issued to the factory and they can duplicate it flawlessly.

Unfortunately, Color Anodizing is not so flawless when it comes to color matching. The anodizing process does not allow for the exact matching of a color since most of the colors (7 in our facility) are produced based on the length of time the material is set into the anodonic bath. Chemicals influence the difference between Clear Anodized and Gold, however the range between Champagne and Black is based on the length of time a product is left to setup in the tank. This process can thus produce many “shades” along the same rainbow of the basic color of Bronze. Many anodizers do not produce a Black Anodized; they only go to Dark Bronze as their darkest color. Some may call Black, “Dark Bronze” or vice-versa.

We offer a sample bar to show the several Anodized colors, however the anodizer has the right to return material to us within a certain “range” of color. This is what I often refer to as a “variation in shade.” A Light Bronze can push the very limit of medium bronze while in another run it can have a shade variance that is closer to the lighter champagne color.

Variation in shade can be attributed, but not limited to the following factors:

1. The exact aluminum alloy of the product being anodized may cause some variations. Some aluminum trims have a different alloy depending on what their particular use might be.
2. The current exterior temperature of the anodizing facility can cause variations. Most anodizing facilities operate in an “open-air” manner due to the chemicals involved in the anodizing process (this is true for our anodizer). This means that the tank temperature can be influenced by the extreme hot or cold climate that a facility may be subject to.
3. The differences in production practices between one anodizing facility and another can cause variations. This is the most common cause in color variation that we have experienced, which is why we try to utilize only one facility for all of our anodizing production.

Written By: Gary Jayne