Directional and color shade variation with Anodized Aluminum

By Steven Soderberg, Lorin Industries, Inc.

Aluminum is a natural material and one of the most abundant minerals found throughout the earth’s crust. Being a natural material, there are many steps or processes to go through to take it from its natural form to that of an anodized grade of aluminum. The last steps in the process of producing aluminum coils that can later be anodized, involve the casting, heat treating and rolling of the metal into its final form.

Like many other natural decorative materials such as wood, copper and other metals, the beauty of the material comes from the natural individuality of the material. While the control of this natural variability is limited based on the alloying chemistry used to create the aluminum, there are steps which can be done to reduce variability when one is looking for more consistency in the product.

Like other products, paint, fabrics, leather etc., when you want a reduction of variability you want to use one lot of material, or consecutive lots of the material for a more consistent process and appearance.  Some steps which can help assure a more consistent visual product are:

  • Order all of your material from the same lot or consecutive lots.
  • Since this product is rolled to the final thickness, each pass in the rolling process does have an effect on the appearance. The thinner the gauge the more times it goes through the rolling process. The rolling affects the surface by rolling/pressing the surface down further into the material sub-surface.  Different gauges of the same alloy will have a different appearance as they will have gone through different processes.
  • The rolling also creates a directionality to the material that can create a difference in appearance when sheets are turned 90-180 degrees from each other.
  • Aluminum oxide is a crystalline structure that is translucent, not transparent. When anodizing you are building an anodic layer on the aluminum. This aluminum oxide layer, like a crystal, will reflect and refract light differently with thickness, giving it a slightly different appearance based on the anodic layer thickness. Design architects typically appreciate how this crystalline structure creates a 3-dimensional effect that helps the building come alive.
  • Variation in the anodized aluminum appearance can be better controlled by keeping this in mind. Same lot or consecutive lots is the first and most important step. So for consistency, definitely all material should come from the same casting house and rolling mill.  After that consistent gauge, and anodic layer thickness are the next most important elements for consistent appearance.
  • The more variation you introduce into the processing of the material; the more variation you will introduce into the appearance.
  • Forming the anodized aluminum is an example of a process that can create variation because of how it can alter the anodic layer. This can change how it reflects and refracts light which can alter its visual characteristics. This could be made more apparent when combining differently formed panel types in close proximity.

In summary, aluminum is a natural material with surface characteristics and potential variations that are enhanced in the anodizing process. To avoid unwanted variation beyond what is natural, simply follow the steps listed above. Then, you can allow your creativity in using the material to create beautiful natural effects to make your project truly stand out.