Chemical Film vs. Anodize

It’s been a while since we’ve posted, so we figured we would give you a post relative to what we have seen recently in manufacturing. For some reason, we have been seeing a lot of engineers who are calling out the incorrect finish for their parts, and we want to help set the issue straight! Simply put, chemical film (also known as chromate conversion, yellow iridite, or alodine) and anodize are NOT the same thing. Most people assume that they may have similarities, that they can be used interchangeably, but this is not the case for most instances. So let’s take a close look at what each finish is and when you should use them. But first, I’d like to point out and say that although we are a metal fabricator, we actually have an in-house metal finishing shop as well as a sister metal finishing company, and have knowledge on when and when not to use each of these finishes. Chemical Film: is a chromate conversion coating which is applied to aluminum parts in order to enhance corrosion protection while still maintaining conductivity. It is also used to prepare aluminum parts before primer and paint to improve better adhesion.Chemical film is often used for parts in the aerospace, defense, medical, high technology, and electronic  industries. Used for heat sinks, automotive wheels, aluminum components, and aerospace enclosures.

There are two widely used classes of chemical film:

  • Class 1A: Offers increased corrosion resistance and adhesive properties.
  • Class 3: Offers increased corrosion resistance and adhesive properties and maintains electrical conductivity. Color ranges from light to dark yellow or gold

Anodize: is a coating which is very common finish for aluminum parts, which is used to make aluminum durable, hard, abrasion resistant, long lasting, and corrosion resistant. Therefore, it’s widely used for esthetic purposes as it won’t chip and the color lasts indefinitely. Anodize is often used for parts in the retail, architectural, commercial, and automotive industries.

There are three types of anodize:

  • Type I: “not common” This type produced a clear to gray coating. Used for electronic applications, fasteners, and parts to be painted.
    • Class 1: Non-dyed
    • Class 2: Dyed (not suitable for colors)
  • Type II: “regular” A sulfuric acid that offers corrosion resistance, moderate durability, creating rich colors, and electrical insulation. Used for machined parts, firearms, tooling, marine, auto, and consumer products.
    • Class 1: Non-dyed
    • Class 2: Dyed
  • Type III: “hard anodize” Offers wear-resistant coating with excellent corrosion and abrasion resistance. Color is light to dark gray and may have color dyed. Will cause coating thickness. Used for machined wear parts, firearms, plastic tooling, gauges, cylinders, assembly equipment.
    • Class 1: Non-dyed
    • Class 2: Dyed

Here is a table showing which finish has important characteristics:

  Chemical Film Anodize
Colors Available Gold, Clear Many
Conductive Yes No
Corrosion Resistance Yes Yes
Affects Part Dimensions No Type 3: thickness .002” nominal
Increased Adhesion Yes No
RoHS Compliant Clear only Sulfuric anodize without Dichromate Seal


We hope this clears up any confusion between the two types of finishes and when they’re applicable. If you are looking for a quality metal fabricator who offers metal finishing, be sure to contact us today for a quote! We specialize if sheet metal, machining, and welding with an in-house paint shop. If you have questions or if you are looking to learn more, be sure to comment below!


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