Guide
Clear anodized aluminum: what color is it on 6061 and 7075, and how should you call it out?
Clear anodized aluminum is aluminum that has been given a sulfuric acid anodic oxide film with no dye, then sealed, so the part keeps the color and texture of the metal underneath. On 6061 it usually looks matte silver-gray, 7075 can pick up a faint yellowish tint as the film gets thicker, copper-rich 2xxx alloys tend toward yellow, and high-silicon alloys turn dark gray. On a drawing it is normally called out as anodize per MIL-A-8625F, Type II, Class 1, sealed, with any thickness and appearance limits added in the note.
By Saola Manufacturing engineering team · Published · Updated
This guide is for design engineers and buyers who put “clear anodize” on a machined aluminum part and want to know what will actually come back. It covers the expected appearance alloy by alloy, the callout that removes guesswork, why lots do not always match, how the machined surface shows through the film, and when chem film or bare metal is the better answer. The anodizing step on a CNC part is normally done by a specialist finisher after machining, so everything here is written as specification guidance you can put on the drawing and the purchase order.
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What color is clear anodized aluminum?
Clear anodized aluminum has no added color: it shows the base metal through a transparent to translucent oxide film, so it looks metallic silver with a slightly softer, grayer tone than bare machined aluminum. The exact shade comes from the alloy, the surface prep and the film thickness, not from the anodizer.
The anodic film is grown out of the aluminum itself, so it is not a paint layer that hides what is underneath. Pure aluminum gives an almost colorless film. Alloying elements such as copper, silicon, iron and manganese do not convert to oxide the same way, and the particles they form in the metal leave a tint, a haze or tiny voids in the film. MIL-A-8625F says this outright for Class 1: natural coloration that results from anodizing the various alloy compositions, and the characteristic color left by sealing, are not counted as coloration (MIL-A-8625F). In other words, a clear anodized 7075 part that comes back faintly yellow is still conforming Class 1, unless your drawing says something more.
The terms buyers search for mean the same coating. “Clear anodize”, “natural anodize”, “clear coat anodize” and “undyed anodize” all describe a Type II sulfuric acid film without dye, which MIL-A-8625F calls Type II, Class 1. “Satin” or “matte” clear anodize is the same film over an etched, brushed or blasted surface; satin describes the texture of the metal, not a different coating. “Clear hard anodize” is a Type III, Class 1 film, and despite the name it is not clear: hard coat comes out light gray to dark bronze depending on alloy and thickness.
How does clear anodize look on 6061, 7075, 2024 and cast aluminum?
The fewer impurity and alloying particles in the metal, the clearer and brighter the film: 6061 typically comes out matte silver-gray, 7075 is usually clear but can show a faint yellowish tint on thicker films, copper-rich 2xxx alloys lean yellow, and high-silicon alloys go dark gray. If two parts must match, make them from the same alloy and product form.
The Aluminum Anodizers Council alloy reference rates the 5xxx and 6xxx series as giving clear films with good protection, the 2xxx copper alloys as yellow with poor protection, the 4xxx silicon alloys as dark gray, and the 7xxx zinc alloys, 7075 included, as clear with good protection (AAC Technical Bulletin 4-13). A second AAC reference adds that the chromium in 6061 and 7075, and in 5052, gives thicker anodic films a yellowish tint (AAC anodic coating designation reference). The same reference lists 6061 and 7075 as non-anodizing-quality grades. That does not mean they anodize badly; it means they are not produced with the tighter impurity control of the “anodizing quality” grades such as 5005, 5657, 6063 and 6463 that architectural work uses when appearance matters across hundreds of panels. For a machined part made from 6061-T6 or 6061-T651 bar or plate, the practical result is usually a matte silver-gray, and a small visible difference between bars from different mill lots is normal. Do not assume 7075 will look darker than 6061: the iron and silicon in 6061 also dull the film, and on some parts 7075 or 2024 comes out the more silvery of the two. Only a sample in the production alloy settles it.
| Alloy | Copper, % | Zinc, % | Silicon, % | Iron, % | Typical clear Type II appearance |
|---|---|---|---|---|---|
| 5052 | 0.10 max | 0.10 max | 0.25 max | 0.40 max | Clear silver; thicker films can turn slightly yellowish |
| 6061 | 0.15–0.40 | 0.25 max | 0.40–0.8 | 0.7 max | Matte silver-gray; small lot-to-lot shift; thicker films can turn slightly yellowish |
| 7075 | 1.2–2.0 | 5.1–6.1 | 0.40 max | 0.50 max | Usually clear; thicker films can show a faint yellowish tint |
| 2024 | 3.8–4.9 | 0.25 max | 0.50 max | 0.50 max | Tends toward yellow (2xxx series); weaker corrosion protection |
Cast and die-cast alloys sit outside that table because their silicon content is far higher than any wrought grade shown. Silicon particles do not convert to oxide, so the film on these alloys typically comes out dull, dark gray and uneven; the AAC reference already rates the wrought 4xxx silicon alloys as dark gray, and casting alloys carry more silicon still. If a cast housing must look like the machined 6061 cover bolted to it, clear anodize will not get you there; see anodizing die-cast aluminum for the options. Temper also has a small effect: heat treatment changes how the alloying elements are distributed, so a T6 part and an annealed part of the same alloy can differ slightly in tone.
If a 7075 part must sit next to a 6061 part on a visible face, either accept the mismatch in writing, move both parts to the same alloy, or change both to a dark dyed color, where alloy tint is least visible. The strength side of that trade is covered in 6061 vs 7075 for CNC parts.
How do you call out clear anodize on a drawing?
Write “Anodize per MIL-A-8625F, Type II, Class 1, sealed” and add a thickness range only if fit or corrosion needs one; the thickness table in the notes section of MIL-A-8625F (paragraph 6.10.5, Table IV) gives 0.00007 to 0.0010 in (1.8 to 25 µm) for Type II. Then add what the specification leaves open: cosmetic faces, surface prep, masking and the appearance standard.
MIL-A-8625F controls a Type II film by coating weight rather than thickness, requiring at least 1,000 mg/ft² before dyeing or sealing (paragraph 3.7.1.1, Table I), and paragraph 3.8.1 requires Type II coatings to be completely sealed unless the contract, order or drawing says otherwise (MIL-A-8625F). Sealing closes the pores and is what gives the coating its corrosion resistance; an unsealed film is only ordered on purpose, usually as a base for paint or adhesive. Under paragraph 4.5.3.1, sealed test specimens are exposed to 5 percent salt spray per ASTM B117 for 336 hours and must then meet the pitting limits of paragraph 3.7.1.2. Architectural and consumer work often uses the Aluminum Association designations instead, where A21, A31 and A41 are the clear designations in three thickness bands (Aluminum Anodizers Council).
| Callout | Film thickness | Typical use on machined parts |
|---|---|---|
| MIL-A-8625F Type II, Class 1, sealed | 0.00007–0.0010 in (1.8–25 µm); coating weight 1,000 mg/ft² min | Default clear anodize for enclosures, brackets, panels |
| MIL-A-8625F Type IIB, Class 1 | 0.00002–0.0007 in (0.5–18 µm), range shared with Types I, IB and IC; coating weight 200–1,000 mg/ft² | Thin film, fatigue-sensitive parts |
| AA A21 (clear, protective/decorative) | under 0.4 mil (10 µm) | Indoor consumer and instrument parts |
| AA A31 (clear, Architectural Class II) | 0.4–0.7 mil (10–18 µm) | Interior and light exterior exposure |
| AA A41 (clear, Architectural Class I) | 0.7 mil (18 µm) and thicker | Exterior exposure, heavy handling |
| MIL-A-8625F Type III, Class 1 (“clear hard”) | 0.0005–0.0045 in (13–114 µm) | Wear surfaces; color is gray to bronze, not clear |
A complete clear anodize note, to adapt rather than copy:
- Anodize per MIL-A-8625F, Type II, Class 1 (clear), sealed. Thickness 0.0002–0.0004 in after finish, measured per ASTM B244 on surface A.
- Pre-finish: bead blast all external faces, glass bead, uniform matte; no bright dip.
- Mask threads and bores marked “M”; dimensions marked “F” apply after anodize.
- Appearance per approved sample, same alloy and prep, cosmetic faces marked “A” only.
Thickness matters for fits because only part of a sulfuric acid film grows inward; the rest builds up above the original surface. Published rules of thumb differ, from about one-third outward to about one-half outward, so ask the finisher for the figure their process holds. The anodizing dimensional change guide shows how to size bores and threads for it, and masking for anodizing covers how to mark faces that must stay bare.
Why does clear anodize vary in color from lot to lot?
Because clear anodize has no dye to mask the metal, every change underneath shows: a different mill lot of bar, a different temper, a longer etch or a thicker film all move the shade. The specification accepts that variation, so if lots must match, the purchase order has to say so.
The main sources, in the order they enter the process:
- Material lot and product form. Two heats of 6061 can both sit inside the composition limits and still differ in iron and silicon content, which shows as a slightly whiter or grayer film. Extruded bar, rolled plate and cold-finished rod also have different grain structure near the surface.
- Surface prep. Caustic etch time, bright dip and blast media change how much light the surface scatters. A longer etch reads lighter and flatter; a bright dip reads glossier and darker.
- Film thickness. Thicker films look slightly darker and more gray, and on alloys such as 7075, 6061 and 5052 any yellowish tint becomes more noticeable as the film thickens. Rack position matters, because outside faces and edges grow more film than recesses.
- Sealing. A hot water or nickel acetate seal leaves a faint characteristic tone that MIL-A-8625F treats as non-dyed. A dichromate seal, still seen on some older drawings, leaves a yellow-green tint and contains hexavalent chromium.
- Grain direction and viewing angle. The film is translucent, so a brushed or rolled surface looks different when turned through a right angle, and two parts can match from the front and split at a glancing angle.
The control method is the same as for dyed parts: approve physical samples made from the production alloy, product form and prep, and require parts that sit side by side to be anodized in the same lot. The anodize color matching guide explains how to set up limit samples and viewing conditions.
How do machining marks, bead blast and brushing show through clear anodize?
Clear anodize reproduces the surface it is grown on and often makes it more visible, so tool marks, step-overs and scratches that are faint on bare metal show plainly after anodizing. Decide the texture before anodizing, with a blast, brush or etch, and write it on the drawing.
The film is thin and translucent, so it cannot fill or level a surface the way paint or powder coat does. Light reflects from both the top of the film and the metal beneath it, which tends to emphasize directional features. That is why a machined face with visible tool paths usually looks more patterned after clear anodize, not less, and why the Aluminum Association system describes a finish by its mechanical (M) and chemical (C) steps as well as the anodic coating (A) (Aluminum Anodizers Council).
| Surface before anodize | AA code | How it looks after clear anodize | What shows through |
|---|---|---|---|
| As machined, no prep | M10 | Bright to semi-bright silver; tool paths more visible | Every step-over, tool change, handling scratch and burr line |
| Bead blast (glass bead) | M4x group (nondirectional textured, e.g. M42 fine matte) | Uniform satin matte, light gray silver | Hides fine tool marks; deep marks and steps still read |
| Brushed or grained | M32 (medium satin, directional) | Linear satin; changes with viewing angle | Brush direction; mismatched grain between parts |
| Caustic etch only | C22 (medium matte etch) | Soft matte, slightly whiter | Softens fine marks; can show grain and alloy streaks |
| Bright dip | C31 or C32 | Glossy, mirror-like to diffuse bright | All scratches and machining marks at full contrast |
For most machined enclosures and covers, a bead blast before clear anodize gives the most forgiving and repeatable result, because it replaces tool marks with a uniform texture. Blast media, pressure and coverage still need to be held steady or the matte level will shift between lots; bead blast vs sandblasting covers media choice and edge protection. If the design calls for an as-machined look, ask for a surface roughness on the cosmetic faces and approve a sample, since the anodizer cannot remove marks the machining left. On the machining side, that means the toolpath and finishing passes on CNC milling have to be planned with the cosmetic faces in mind before the part ever reaches the finisher.
When should you choose clear anodize instead of chem film or bare aluminum?
Choose clear anodize when the part needs wear and corrosion protection with a metallic look and does not need electrical contact on the coated faces. Choose chem film when the part must stay conductive or will be painted, and leave it bare only for internal parts in a dry environment.
Anodic films are electrical insulators, so a clear anodized face will not ground a chassis or shield an enclosure without masking or a contact feature; chem film per MIL-DTL-5541F Class 3 exists for exactly that case (MIL-DTL-5541F). The comparison below puts the trade in one place.
| Property | Clear anodize (Type II, Class 1, sealed) | Chem film (Type II, Class 1A or 3) | Bare machined aluminum |
|---|---|---|---|
| Appearance | Metallic silver, slightly gray; alloy tint shows | Clear to faint iridescent; can look patchy | Bright metal, dulls and stains with handling |
| Film thickness | 0.00007–0.0010 in (1.8–25 µm) | Very thin, no practical dimensional change | None |
| Neutral salt spray requirement | 336 h | 168 h | No requirement |
| Electrical conductivity | Insulating | Low contact resistance (Class 3) | Conductive |
| Scratch and wear resistance | Good; harder than base metal | Poor; easily scuffed | Poor |
| Paint or adhesive base | Possible, usually unsealed | Good (Class 1A) | Poor without pretreatment |
| Choose it when | Visible part, handled, indoor or outdoor exposure, no grounding on coated faces | Grounding, EMI bonding, paint base | Internal part, dry environment, cost first |
A common combination on electronics enclosures is clear anodize overall with chem film on masked contact pads, which keeps the look while giving a ground path. The full comparison, including RoHS and dimensional notes, is in chem film vs anodize, and grounding details are in anodized aluminum conductivity and grounding.
What should you send with an RFQ for a clear anodized machined part?
Send the drawing with the full anodize note, the alloy, temper and product form, the cosmetic faces, the surface prep, the masked features and any appearance sample. With that, the machining and finishing plan can be set up together instead of argued about after the first lot.
When we review a drawing that calls for clear anodize, the first questions are which faces are cosmetic, whether parts in the same assembly must match, and whether the dimensions on the drawing apply before or after the film. Anodizing on our parts is done by an outside finisher, so we pass your note through unchanged and ask you to settle anything the note leaves open before the order is placed: the alloy for parts that must match, the blast or brush texture, the thickness band and the masking. If the drawing only says “anodize clear”, we will ask for the type, class and seal rather than guess. Send the STEP and PDF files, the finish note and any approved sample photos through the quote form.
Frequently asked
Is clear anodize the same as natural anodize?
Yes. Clear, natural, undyed and “clear coat” anodize all describe a Type II sulfuric acid film with no dye, which MIL-A-8625F calls Class 1. Ask the finisher to confirm the seal, since an unsealed film is a different product.
Is satin anodized the same as clear anodized?
Satin anodize is clear anodize over a satin surface, usually brushed, etched or bead blasted before anodizing. The coating is the same; the texture under it is what makes it satin, so the drawing should name the prep step.
Is clear anodized aluminum conductive?
No. The anodic oxide is an electrical insulator, so grounding points need masking, a spot-faced contact or chem film on the contact area. See anodized aluminum conductivity and grounding.
Why did my 7075 parts come back yellow?
Alloying elements in 7075 can tint the film; the Aluminum Anodizers Council attributes the yellowish cast on thicker films to its chromium content, and it becomes more noticeable as thickness goes up. That tone is accepted as natural coloration under Class 1, so if the parts must look like 6061, change the alloy or approve a sample showing the acceptable shade.
Will clear anodize hide scratches or tool marks?
No. The film follows the surface and usually makes marks more visible. Remove or blend them before anodizing, typically with a bead blast or brushed finish, and call that prep out on the drawing.
Sources
- MIL-A-8625F, Anodic Coatings for Aluminum and Aluminum Alloys, US Department of Defense, 1993, with Amendment 1 (2003) (paragraphs 3.5, 3.7.1.1 with Table I, 3.7.1.2, 3.8.1, 4.5.3.1, and 6.10.5 with Table IV)
- MIL-DTL-5541F, Chemical Conversion Coatings on Aluminum and Aluminum Alloys, US Department of Defense, 2006
- ASTM B209/B209M-21a, Aluminum and Aluminum-Alloy Sheet and Plate, ASTM International, 2021
- Alloys Suitable for Anodizing (Technical Bulletin 4-13, Aluminum Alloy Reference for Anodizing), Aluminum Anodizers Council, 1994, accessed October 2026
- How to Specify Finishes on Aluminum (Aluminum Association designation system), Aluminum Anodizers Council, accessed October 2026
- Aluminum Association Designation System (full M, C and A code lists), Aluminum Anodizers Council, accessed October 2026
- Anodic Coating Designation System (includes alloy suitability notes), Aluminum Anodizers Council, accessed October 2026