Aluminum Profile Surface Finish Specifications: What to Put on a Purchase Order

Short answer: a purchase order for aluminum profile finishes must convert a vague request (“make it black and nice”) into precise, inspectable requirements for process, colour standard, film-thickness target and tolerance, gloss level, designated cosmetic faces, accepted defect classes, sample and batch controls, packing/protection and an explicit inspection plan. This guide shows what to put on the PO and why, and what it does not cover (it does not replace a tested system performance report, structural engineering checks, whole-window U-values, or supplier capability audits).

Choose the surface process and state the required specification

First decision: be explicit about the process. “Anodized” and “powder coated” are different families with different inputs, tolerances and failure modes. On the PO name the process (for example, decorative anodize, hard anodize, or epoxy/polyester powder coat), and reference the specific workmanship or process standard you will accept.

Use precise language on the PO such as: “Anodize — decorative architectural, clear, Class A film, sealed per supplier standard with verification per ISO 7599:2018” or “Powder coat — TGIC Polyester, thermoset, oven-baked.” If you expect a supplier service, link to their service page in the inquiry (for example, request the supplier’s Anodizing Service or Powder Coating Service), but still list the PO-level acceptance criteria below.

Specify colour, gloss and how colour will be evaluated

Colour must be an objective reference: RAL, BS, Pantone, supplier chip number, or a calibrated spectral sample. If colour matching matters, require a spectrophotometer report (CIE Lab) and specify the delta E method you will accept (for example, CIEDE2000). If the colour is tolerant, say so; otherwise require a pre-production sample or batch sample approval.

Gloss affects perception and durability. Always specify the measurement geometry (60° is common for general purpose; 85° for matte). If you need both appearance and cleanability requirements, include both a gloss target and acceptable tolerance.

Film thickness targets and measurement method

Film thickness correlates directly to protection and appearance. Give a target and an allowable tolerance and state the measurement method (eddy current, coulometric for anodize, destructive cross-section if required). Because practices vary, present thickness as a project decision, not a universal value.

On the PO state the exact measurement locations and sampling frequency (for example: “Measure film thickness at six representative locations per profile per batch; report mean, min, max and locations.”). If you accept non-destructive gauges, name the gauge class or method.

Define cosmetic faces, allowable defects and acceptance levels

A frequent failure mode is disagreement about which faces are cosmetic. On the drawing mark cosmetic faces and also include a written list on the PO. Specify acceptable defect classes for each face: “A — showroom/cosmetic (no visible defects at 1 m under D65 daylight), B — assembly face (minor tool marks allowed), C — machined/hidden (no coverage required).”

Include lighting conditions and viewing distance in the PO when appearance matters. If a defect-rating photograph is accepted, include a reference image or supplier-approved gallery.

Colour evaluation, samples and batch control

Require physical samples for initial signing off: either a manufactured pre-production part or a supplier’s certified chip sample. For production, require either per-batch spectrophotometer data or statistical sampling and a retained sample for cross-checking.

If colour matching between anodize and powder coat is required, say so and define the allowed Delta E using a named method (for example, CIEDE2000). If you need guidance on the fundamental trade-offs between processes, read a direct comparison in the guide on anodizing vs powder coating and see how anodized colour variation occurs in field practice via anodized aluminium colour variation.

Protection, packing and handling instructions to reduce finish damage

Specify protection film type, removal instructions and allowed time-on-profile. Also state edge protection, separators, and pack configuration to avoid rub-through during transport. Include labeling for orientation, “cosmetic face up”, and unpacking instructions for installers.

Put removal timing and responsibility on the PO. If onsite trades will remove protective film, note the installer’s responsibility to avoid scuffs and the rejection criteria for film residues.

Inspection and documentation to require on the PO

Specify which inspections are mandatory, their sampling plan and the documentation to be delivered with each batch: inspection checklist, thickness readings, colour report, photos of each batch, non-conformance reports if any, and a Certificate of Conformance referencing the PO number.

If you will accept supplier internal inspection only, require evidence: signed inspection sheets and digital photos. If you require third-party or buyer inspection, state that explicitly and give the window for inspection prior to shipment.

Worked Specification or Review Example

Below is a worked PO-level finish specification for a hypothetical architectural profile. All numeric values are illustrative assumptions for review and must be adapted to project requirements and supplier capability; they are not product guarantees.

PO line: 1000 pcs — extruded profile X123 — finish

Process: Decorative anodize, clear.
Reference standard: Supplier shall perform decorative anodizing in accordance with supplier process; finish acceptance per ISO 7599:2018 where applicable. Buyer requires pre-production sample.

Colour: Clear anodize (no dye). If dyed, the buyer will specify RAL code in writing.

Film thickness (illustrative assumptions): Target 12 µm; allowable: 10–14 µm measured by coulometric method at 6 locations per part. Report mean, min, max.

Sealing: Hot water seal per supplier standard; report seal method and soak time.

Cosmetic faces: See drawing sheet A2; faces marked ‘A’ are cosmetic. Acceptance: no visible defects at 3 m under D65-equivalent lighting. Faces B and C accept functional tool marks.

Gloss: Not specified for clear anodize; if dye or mechanical polish applied, buyer will issue a separate gloss spec (@60°).

Samples: PFS (pre-finishing sample) required — 3 full-length samples to be produced and approved before first production run.

Inspection: Per inspection checklist — visual, film thickness, adhesion spot check (coulombic or rated test), photographs of each pallet. Supplier to provide digital report and C of C with each shipment.

Packing: PE film low-tack removed by installer; cardboard separators between profiles; pallet strap ends cushioned. Label each pallet with PO and batch number.

Non-conformance handling: Reject on visible damage to cosmetic faces; supplier to segregate and supply rework plan.

Notes: Numeric film thickness target above is an illustrative assumption; buyer must agree final targets prior to PFS sign-off.
  

What to Send with Your Inquiry

To get an accurate quotation and a correct PO write-up, send the following items with your inquiry. Each item reduces assumptions and the risk of rework.

• 2D drawings (PDF) with all faces dimensioned and cosmetic faces clearly flagged.
• 3D CAD models (STEP or Parasolid) for complex profiles — helpful for masking and fixtures.
• Quantity, expected production cadence (one-off, batch size, repeat schedule).
• Desired finish process and reference links if you have them (for example, a link to an industrial extrusion series or supplier finishing service).
• Any reference colour chips or digital spectral files; if none, state the reference system (RAL, BS, Pantone) and tolerances.
• Sample part or piece-part photograph if available; if colour-critical, include an approved master sample.
• Packing and protection requirements — film type, separation, palletization orientation and maximum allowed stacking.
• Inspection requirements — sampling plan, required reports (photos, spectrophotometer data, thickness logs), and who will perform inspection (supplier, buyer, third-party).
• Any required standards to be considered (list them) and deadlines for pre-production sample approval.
• Special processes: masking for post-machining, rework allowance, or secondary operations like CNC (link to CNC machined parts if relevant).

Frequently Asked Questions

1. Can I specify a Delta E number for anodize?

Yes, you can specify a Delta E tolerance and the measurement method (CIEDE2000 preferred for small differences). However, anodized surfaces have intrinsic microstructure and local thickness-related variation; treat Delta E limits as project-dependent and require pre-production samples to verify feasibility.

2. Should I specify film thickness as a single number or a range?

Specify a target plus allowable tolerance and name the measurement method and locations. A range or tolerance recognizes process variability; single-number zero-tolerance is not realistic in production.

3. How do I handle machined features after finishing?

Decide whether finishing is before or after machining. If finishing precedes machining, also specify rework methods and acceptable appearance for machined faces. If finishing follows machining, specify masking areas and post-finish touch-up allowance.

4. Do I need salt spray or accelerated corrosion testing on the PO?

Only if the project requires it. If you require salt spray testing, reference the test method explicitly (for example ISO 9227) and specify whether tests are production-batch tests, type tests, or supplier qualification tests.

5. What should I do if the supplier proposes an alternative process?

Require the supplier to provide comparative data, pre-production samples and an updated inspection plan. Make acceptance contingent on sample approval and written agreement on any performance claims.

6. How do I control colour drift between batches?

Require batch spectrophotometer readings, retain reference samples from each batch, and include acceptance criteria for color metrics. Define what constitutes a batch and how cumulative tolerance is managed for multi-batch orders.

7. Can gloss be measured after installation?

It can, but environmental exposure and handling will affect gloss. Prefer measurement at supply stage with controlled lighting and instrument calibration. If measured onsite, require calibration and method details in the PO.

Links to further technical discussions

For powder-coating failure modes and common defects, see the technical note on powder coating defects on aluminum profiles. Use these references when you draft acceptance criteria and inspection checklists.

Technical Reference and Scope

Relevant international standards you may reference on a PO (buyer to verify applicability and edition for the specific project):

• ISO 6362-4:2022 — Tolerances and other requirements for extruded aluminium profiles (confirm applicability to your profile series).
• ASTM B221-21 — Standard specification for aluminum and aluminum-alloy extruded bars, rods, wire, profiles, and tubes.
• ISO 7599:2018 — Anodizing of aluminium and its alloys — General specifications and quality requirements for decorative anodic oxidation coatings (verify the exact clause for your use).
• ISO 9227 — Corrosion tests in artificial atmospheres — Salt spray tests (refer to the specific test method if you require salt spray testing).

Scope limitations: citing the standards above does not imply product compliance without documented test results and traceable inspection records. These standards govern test methods, material and process boundaries; they do not replace an agreed supplier process control plan, pre-production sample approval, or a site-specific performance test of the assembled system.

Final reminder: every finish requirement you give should be measurable, assignable to a party (supplier or buyer), and tied to a sample or acceptance plan. Where you leave choices vague, the supplier will interpret them — and that is the most common root cause of disputes.