linetec Anodize Finishes Tampa Art Museum



Anodizing successfully combines science with nature to create one of the world’s best metal finishes. Anodizing is the process of electrochemically controlling, accelerating and enhancing oxidation of an aluminum substrate. The anodizing process, because it is an integral part of the substrate, produces an oxide film that is uniform, hard and protects the rest of the aluminum substrate from deterioration – providing excellent wear and abrasion resistance with minimal maintenance in most environments.


The coating produced is extremely durable, and the hardness of the surface is comparable to a sapphire—the second hardest substance on earth. This characteristic makes anodize an excellent choice for use in high-traffic areas where resistance properties are important.

Anodized aluminum resists the ravages of time, temperature, corrosion, humidity and warping, adding to its long life cycle. Anodized aluminum is an inert material that is not combustible, 100% recyclable and poses no health risks


The typical anodizing employed in the architectural industry is called two-step electrolytic. The actual anodizing and coloring of the aluminum occur in separate steps of the process. The anodizing step takes place in a tank that contains a solution of sulfuric acid and water. The tank is charged with electrical current, and aluminum oxide is formed on the surface of the aluminum.

anodize finish process electrolytic

After anodizing is complete, the parts can be immersed in an optional coloring tank, to achieve champagne, bronze tones or black instead of the standard clear or silver finish.

In the coloring tank, the anodized aluminum is immersed in a bath containing an inorganic metal such as tin, cobalt or nickel, which is deposited in the anodic pores by means of electrolytic current. The amount of time the part is immersed will determine the color achieved. Darker colors are created by extending the immersion time and increasing metal deposition. The anodize colors typically seen on architectural products range from champagne to dark bronze to black.

anodize finish process MSU classes

Class I and Class II anodic coatings are designations created by the Aluminum Association for the purpose of codifying the specification of anodized aluminum.

Class I coating has a mil thickness of 0.7 (18 microns) or greater

Class II coating has a minimum mil thickness of 0.4 (10 microns)

Class I coating is a high performance anodic finish used primarily for exterior building products and other aluminum that must withstand continuous weathering and outdoor exposure.

Class II coating is a commercial anodic finish recommended for interior applications or light exterior applications receiving regularly scheduled cleaning and maintenance such as storefronts.

Coating thickness can be measured by an “eddy current”, a nondestructive test instrument, or by cutting a cross-section of the anodized aluminum, mounting it in a slide, polishing the edge, and reading the coating thickness directly with a microscope.

Class I and Class II coatings should not be confused with Type I, Type II, and Type III anodic coatings as described in the authoritative anodizing standard, MIL-A-8625. Type I anodize refers to chromic acid anodizing. Type II is normal “clear” sulfuric acid anodizing. Type III is “hardcoat” using sulfuric acid or mixed chemistry electrolytes.

COATING WEIGHT SPECIFICATION:Class I >+ 27.0 mg/in2Class II >= 15.5 mg/in2
COATING DENSITYClass I >= 38.0 mg/in3Class II >= 38.0 mg/in3

All Linetec anodize finishes are a Class I coating, with the exception of ANO-204 Clear, which is a Class II coating. Clear anodize is available in both Class I and Class II. Class I anodize coatings are the only finishes that carry a warranty.

linetec anodize finish process longlasting


Class I anodize is used on the exterior of architectural projects. It has a higher mil thickness than Class II anodize; it is more resistant to salt spray and the sea coast; and it is more durable in high traffic areas.

Class I anodize, with a minimum mill thickness of 0.7 (18 microns), can be a suitable choice for coastal climates as it possesses exceptional resistance to corrosion, discoloration and wear; however, its natural beauty can be marred by harsh chemicals, rough conditions or neglect. These conditions may only affect the surface finish and not reduce the service life of the aluminum, but mortar, cement, and other alkaline materials will quickly corrode an anodize finish if allowed to dry on the metal surface.

Class I anodize meets or exceeds all requirement of AAMA 611 “Voluntary Specification for Anodized Architectural Aluminum.

anodize finish process environmentally friendly

Environmentally-Friendly Anodize Etching Process

Class I anodize meets or exceeds all requirement of AAMA 611 “Voluntary Specification for Anodized Architectural Aluminum. Linetec’s Anodize offers a more environmentally-friendly product with our anodize etching technology.

Eco friendly anodize creates an aesthetically appealing “frostier” appearance that helps hide small defects, such as die lines, minor corrosion and scratches, that may occur on the aluminum surface.

Hardness Second Only To The Diamond

The anodizing process thickens the natural oxide film resulting in a heavy aluminum oxide film of controlled thickness having the hardness similar to that of a sapphire (second hardest substance known to man, second only to the diamond).

learn more about the linetec anodize environmentally-friendly process


The performance strengths and limitations of anodize are summarized as follows:

Strengths of Anodize

  • Color stability
  • Exceptional hardness, compared to a sapphire
  • Durability and abrasion resistance
  • Anodize protects and maintains the structural integrity of the aluminum
  • Non-hazardous, produces no harmful or dangerous by-products
  • Ease of maintenance
  • Excellent weatherability (Class I)
  • Metal appearance

Limitations of Anodize

  • Limited color choices
  • Difficult touch up
  • Color may vary depending on alloy & trace elements in aluminum
  • Surface imperfections of the aluminum may show through the anodize


Anodic films are very hard, and as a result, most post-production bending of anodized aluminum causes the film to “craze,” which produces a series of small cracks in the finish. It is recommended that all forming and bending be done prior to anodizing.

Flat sheets must have a thickness of .040 to be anodized.

An anodize coating actually becomes part of the aluminum, rather than adding a thin layer over the aluminum part as with a paint coating. Therefore gouges, scratches and die lines can be enhanced by an anodized finish. However if eco-friendly anodize is utilized, the etching process will give the aluminum a frostier matte finish that will hide the irregularities and small scratches on the aluminum surface.

Anodize touch-up should not be needed in most cases because anodizing is so hard that it is not easily scratched. Touch-up paint should be used extremely sparingly over anodize. Only the visible raw aluminum in the scratch or gouge should be touched up with matching paint (Alodine pretreatment should be applied first). In most cases, the match will not be ideal as anodizing is a transparent to translucent coating while paint typically is opaque and will not blend in.

Other fixes include:
Replacing the damaged piece with a new one
Cladding the damaged piece with another anodized piece
Clean, pretreat and paint the entire assembly.

None of these “other fixes” are good ones. The best repair is not to allow the material to get damaged in the first place. The number one cause of damage on the jobsite is not protecting the anodized material from harsh chemicals such as concrete/mortar or muriatic acid/brick wash. If reasonable care is taken during handling and high and low pH chemicals can be avoided, repair and/or touch-up of an anodize finish will not be needed.

We sure do! You can request samples here.

AAMA Verified Component Licensee

American Architectural Manufacturers Association, a material-neutral organization, is the source of performance standards for the fenestration professionals of window, door, skylight, curtain wall and storefront manufacturing companies.


As your Single Source Solution we offer custom options and specialty finishes such as Wood Grain Finishes, Copper Anodize, Spattercoat and textured Terra Cotta Coatings.


Linetec has earned a long-standing reputation as a leader in environmentally-conscious practices and finishing options. For more than a decade, environmental responsibility has been written into our core values.


Our technical experts at Linetec provide valuable industry education of high-performance architectural finishes to architects, engineers, specifiers and manufacturers.

Photo credits:Tampa Museum of Art, Super Sky Products Intl
linetec architectural finishing