Select Page

Sulfuric Anodizing

We provide Sulfuric Anodize with the following options. Type ll Clear (Class1) and Type ll Dyed (Class ll), as well as Type III hardcoat.


Sulfuric acid is the most widely used solution to produce the anodized coating. Coatings of moderate thickness (0.00007″ to 0.001″) are known as Type II, as named by Specification . Very thin coatings similar to those produced by chromic anodizing are known as Type IIB.


Sulfuric anodizing increases the material’s wear resistance, corrosion resistance, ability to retain lubricants and PTFE coatings, and electrical and thermal insulation. Standards for thin sulfuric anodizing are given by MIL-DTL-8625 Types II and IIB, class 1 (undyed) or class 2 (dyed), AMS 2471 (undyed), and AMS 2472 (dyed). Coatings thicker than 25 μm (0.001″) are known as Type III, hardcoat, hard anodizing, or engineered anodizing. See our approvals for these processes.

Sulfuric acid on aluminum produces a porous surface which can accept dyes easily. There are a number of dye colors available. However, the colors produced tend to vary according to the base alloy. Though some may prefer lighter colors, in practice they may be difficult to produce on certain alloys such as high-silicon casting grades and 2000-series aluminum alloys. Another concern is the “lightfastness” of organic dyes. Some colors are particularly prone to fading because of the chemistry of the dye. Sulfuric anodizing is usually sealed to reduce or eliminate dye bleed out.


Sulfuric anodizing produce pores in the anodized coating. These pores can absorb dyes and retain lubricants. Long immersion in boiling-hot deionized water or steam is the simplest sealing process. It is not completely effective and reduces abrasion resistance. Teflon, nickel acetate, and hot sodium dichromate seals are commonly used. MIL-DTL-8625 requires sealing for thin coatings (Types I and II) and allows it as an option for thicker coatings (Type III).


Request a quote on sulfuric anodizing for your application, or contact us with any questions.

Clear Anodize Type ll Process

Clear Anodize Type ll Process

Shot Peen + Blast
Chemical Processing
Painting + Spray Coatings
Other Services