Anodize Type II or Type III? A finish guide for engineers

Type II is for color, Type III is for wear. The hard part is knowing which trade-offs you are making with each.

Type II — decorative anodize

Type II builds a 5-25 micrometer aluminum oxide layer over the base metal. The layer is porous (think tiny vertical tubes) which means it accepts dye in any color — black, red, blue, gold, custom Pantone. After dyeing, the pores are sealed in hot water or nickel acetate to lock in the color. Result: a smooth, hard, corrosion-resistant decorative finish that looks premium and feels solid.

Use Type II for consumer electronics, optics housings, fixtures that need to look good, parts where color coding matters. Avoid for sliding wear surfaces — the layer is thin and will eventually wear through.

Type III — hardcoat anodize

Type III builds 25-75 micrometers (some specs go to 100), and the layer is denser. The result is roughly the hardness of mild steel — 60-70 HRC equivalent. Standard color is black or dark grey (the dense layer cannot accept dye well). Use it on sliding parts, gear teeth, engine components, anything that takes mechanical wear.

Trade-off: Type III adds noticeable thickness to your part. A 50 micrometer layer means dimensions grow ~25 micrometers per side. For tight-tolerance features, machine the part 25-50 micrometers undersize before anodizing.

What we tell customers

If your part lives in a drawer, on a desk, or inside an enclosure: Type II. If it slides against another part, gets dropped on concrete, or sees abrasive wear: Type III. If it is decorative AND wears: Type III in black, then accept the look. If you need both look and function in one finish: consider PVD coating instead, which gives Type-III-like wear resistance with chrome or gold colors.