Anodized aluminum components shown as an illustrative finish example

Technical Resource

Surface Finishing & Coatings Guide

Compare powder coating, Type II and III anodizing, passivation, electroplating and bead blasting by substrate, function and drawing requirements.

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Finish for function first, appearance second

A finish protects the part, changes how it looks, or both. The right choice depends on the base metal, the environment, the look you need and how the part is assembled.

Finishes also affect fit, because most add thickness, and grounding, because many do not conduct. Specify the finish early so the design and tolerances allow for it.

  • Typical thickness ranges, set by your specification
  • Color and gloss agreed with approval samples
  • Coating thickness report on request
Two machined aluminum corner parts with a matte anodized finish

Finish specifications and dimensional effects

Illustrative thickness ranges, not acceptance limits. Specify the coating system and applicable standard on the drawing. Bead blasting is mechanical preparation, not a protective coating.
FinishBase metalThicknessConductsBest for
Powder coatSteel, galvanized, aluminum60-120 umNoDurable color
Anodize Type IIAluminum5-25 umNoThin metallic finish
Hard anodize Type IIIAluminum25-75 umNoWear surfaces
Zinc platingCarbon steel5-25 umYesFasteners, brackets
PassivationStainless steelNo build-upYesAfter machining or welding
E-coatSteel, aluminum15-30 umNoEven cover, primer
Bead blastingSteel, stainless, aluminumNo coating buildBase metal dependentSurface texture preparation

Common finishes at a glance

Color chips are indicative only. Final color and gloss are agreed with approval samples.

  • Zinc plating

    Sacrificial corrosion protection for hardware and small steel parts.

    Best for
    Fasteners, brackets, small steel parts
    Typical use
    Indoor and light outdoor hardware

  • Powder coating

    Durable, uniform color with good coverage on large parts.

    Best for
    Enclosures, frames, guards
    Typical use
    Steel, galvanized steel and aluminum

  • Anodizing

    Hard oxide layer grown from the aluminum surface, clear or dyed.

    Best for
    Aluminum panels and machined parts
    Typical use
    Wear resistance and colored trim

  • Black oxide

    Thin conversion coating with a dark finish, usually oiled.

    Best for
    Steel tools and fasteners
    Typical use
    Low-glare, mild protection indoors

  • Nickel plating

    Hard, bright and wear resistant plated layer.

    Best for
    Steel and brass hardware
    Typical use
    Wear surfaces and decorative parts

  • E-coat or painting

    Even primer coat or custom-color paint system.

    Best for
    Complex shapes and special colors
    Typical use
    Primer for topcoats, low-volume color

  • Passivation

    Chemical treatment that restores corrosion resistance on stainless.

    Best for
    Stainless steel parts
    Typical use
    After machining or welding

  • Brushed or polished

    Mechanical finishing for a satin or mirror surface.

    Best for
    Stainless, aluminum, brass
    Typical use
    Visible faces and easy-clean surfaces
  • Zinc plating
  • Powder coating
  • Anodizing
  • Black oxide
  • Nickel plating
  • E-coat
  • Wet painting
  • Passivation
  • Brushed finish
  • Polished finish

Common drawing callouts

Standards often cited on drawings. Use the one your program requires.
FinishOften specified asAlso state
Powder coatThickness range, RAL colorGloss, texture, adhesion test
AnodizeMIL-A-8625 Type II or IIIClass 1 clear or Class 2 dyed
Zinc platingASTM B633 or ISO 2081Trivalent passivate color
PassivationASTM A967 or AMS 2700Nitric or citric method
E-coatThickness rangeSalt-spray test standard

Powder coating or anodizing

Common alternatives for aluminum enclosures and panels.

Option A

Powder coating

  • Broad color and texture choices
  • Coating build can affect mating dimensions
  • Can be specified for suitable steel and aluminum substrates
  • Threads and contact faces may need masking

Option B

Anodizing

  • Oxide layer formed on aluminum
  • Type II and III have different functional aims
  • Clear or dyed appearance depends on alloy and process
  • Color can vary between alloy lots

Compare coating requirements, wear, appearance, fit and substrate before selecting a finish; confirm sample feasibility during quotation.

How to choose

Match the finish to the base metal first, then to the environment and the look.

  • Carbon steel

    Zinc plating for hardware, powder coat for color, e-coat for complex shapes or as a primer under powder.

  • Aluminum

    Anodize for a thin metallic finish or wear surfaces; powder coat for color matched to steel parts.

  • Stainless steel

    Passivate after machining or welding. Brush or polish where the face is visible.

  • Grounding and contact

    Anodize, powder and e-coat insulate. Mask contact faces or choose zinc or passivation.

  • Tight fits and threads

    Allow for build-up or mask the feature. Passivation and black oxide barely change size.

  • Hardened steel

    For high-strength steel, assess hydrogen-embrittlement risk and specify any required post-plating relief treatment.

What to put on the drawing

Define measurable acceptance criteria with the selected finish and service environment.

Finish name
Process and type, for example powder coat or clear anodize Type II
Thickness
State the required range for the selected finish and application
Color and gloss
A color reference and gloss level, approved by sample
Corrosion testing
If needed, state the salt-spray method, exposure duration and acceptance criteria; test hours alone do not predict field life
Masking
Threads, contact faces and datums that must stay bare
Cosmetic faces
Which faces are visible and the defect level accepted

Surface finishing questions

What is the difference between passivation and electropolishing?

Passivation is a chemical treatment that removes free iron and restores the protective oxide on stainless, with no visible change. Electropolishing removes a thin layer of metal electrically, leaving a bright, smooth surface that is easier to clean. Electropolishing passivates as it works but costs more.

Can zinc plating meet restricted-substance requirements?

A suitable zinc system may be available, but compliance depends on the complete coating chemistry and current declarations. State the applicable requirement on the drawing and request supporting documentation at quotation.

Do finishes change dimensions?

Most do. Powder coat adds the most, while anodizing grows partly into the surface and partly outward. We account for build-up in the design review and mask critical features when needed.

Can a finish match a color reference?

Provide a color reference or sample part. Feasibility, acceptable variation and any approval sample can then be defined for the project.

How do you confirm corrosion performance?

We agree the specification with you first, then confirm the finish and any required test per project. A coating thickness report can be supplied with the parts. We do not quote test results in advance.

Can one order include different finishes?

This can be evaluated during quotation. Separate finishing routes may affect scheduling, packaging and inspection requirements.

Need a finish specified?

Share the base metal, service environment, appearance and fit requirements for a finishing review during quotation.

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