Guide
What is a golden sample, and how do limit samples lock down appearance and fit with a supplier?
A golden sample is a physical part, approved and signed by the buyer, that a supplier and an inspector use as the reference for everything a drawing cannot fully define: anodize or powder coat color, gloss, texture, cosmetic blemishes, and sometimes the feel of an assembly. Limit samples are its companions: parts that show the edges of what is still acceptable, so that the decision at receiving inspection becomes “inside the bracket or outside it” rather than “does this look like the one on my desk?”
By Saola Manufacturing engineering team · Published · Updated
This guide is about the samples themselves as controlled objects: which ones you need, how to choose them from real production variation, how to reference them on the drawing and purchase order, and how to keep them valid across years of reorders with a supplier on another continent. Writing the cosmetic note itself, with surface classes and defect limits, is a separate job; so is setting the sampling plan that decides how many parts get compared against the samples. Both are linked below where they matter.
On this page
Why is a single golden sample not enough to accept parts?
A single golden sample shows the target but not the tolerance, so every production part is judged against one point and any visible difference becomes an argument. Limit samples turn that point into a band that both sides can see and sign.
Dyed anodize is the clearest example. The final shade depends on the alloy and temper, the anodic coating thickness, the dye bath concentration and age, and the sealing step, and none of those is identical from one tank load to the next. Two racks of black-anodized 6061 run a week apart can both be good parts and still look different side by side under shop lighting. If the only reference is one perfect part, an inspector who sees any difference has two choices, both bad: reject good parts, or accept by personal judgment, which drifts over time and differs between your receiving dock and the supplier’s final inspection.
The same logic applies to gloss, to the bead-blast texture under a clear anodize, to the orange peel on a powder coat, and to tool marks on a milled cosmetic face. Each of these varies continuously, and each needs two edges, not one center. The golden sample still earns its place: it is the aim point the process should be centered on, and the part you show a new operator or a new inspector first.
What does a complete golden sample and limit sample set contain?
A working set contains one master at the target, a pair of limit samples for each attribute that varies (light and dark, high and low gloss, fine and coarse texture), and, where defects are the issue, defect boundary samples showing the worst acceptable blemish. A reject sample is optional but useful for training.
Automotive practice already has names for most of these pieces. The AIAG Production Part Approval Process manual lists a master sample and an Appearance Approval Report among its elements, the latter for parts whose design record designates appearance items such as color, grain and gloss (AIAG PPAP, 4th edition). Outside automotive, you do not need the full PPAP package to borrow the discipline: one record per sample, a unique number, a signature, and a stated revision of the drawing it represents.
| Sample | What it shows | How it is used at inspection | Typical copies |
|---|---|---|---|
| Golden (master) sample | The target color, gloss, texture and finish quality | Aim point for the process; first reference for new inspectors | One at the buyer, one at the supplier |
| Color limit pair | Lightest and darkest acceptable shade, or limits on a named hue shift | Production part must fall between the two | One pair per site |
| Gloss or texture limit pair | Highest and lowest acceptable sheen, or finest and coarsest blast texture | Compared at the viewing angle stated on the drawing | One pair per site |
| Defect boundary sample | Worst acceptable scratch, pit, run, mask line or witness mark on a named surface | Anything worse than this sample on that surface class is rejected | One per defect type that recurs |
| Reject sample | A part just outside a limit | Training and calibration of inspectors, never for acceptance | Kept at the supplier |
How should limit samples be chosen for anodize color and gloss?
Pick them from real parts made by the actual production process, spread across several loads, rather than asking the supplier to make deliberately light or dark parts. Limits built from real variation are limits the process can actually hold.
A practical sequence works like this. Run the pilot or first-article lot across more than one anodize load or coating batch, on the alloy and temper that production will use, because anodize color on a casting alloy will not match the same dye on wrought bar; the guide on anodizing die-cast aluminum explains why. Lay the parts out together under the agreed light, choose the one closest to the design intent as the golden sample, then choose the lightest and darkest parts you would still ship to your own customer as the limit pair. If no part is acceptable, the problem is the process or the specification, not the samples, and it is cheaper to learn that now.
State how the comparison is made, because the same pair of parts can look matched under one light and mismatched under another. ASTM D1729 specifies the equipment and procedure for visual appraisal of colors and color differences of diffusely illuminated opaque materials, including the light source and the viewing booth (ASTM D1729); for paint and powder coat films, ISO 3668 describes a comparable booth comparison against a reference standard (ISO 3668). D1729 places metallic and pearlescent materials outside its scope, and ISO 3668 does not apply to metallic-effect coatings unless the lighting and viewing details are agreed separately, so for a bright or polished anodize, which reads more like a metallic surface, write the viewing condition into the sample agreement itself. Checking under two different light sources catches metamerism, where two finishes match under one light and not the other, which happens when a replacement dye or a different coating system is used.
If either party has a spectrophotometer or glossmeter, record readings on the golden sample and the limit pair at the moment of approval. Color difference can be calculated and reported per ASTM D2244 (ASTM D2244), and specular gloss of a nonmetallic finish such as powder coat is measured at a stated glossmeter geometry per ASTM D523 (ASTM D523). Anodized aluminum has its own gloss and reflectance method, ISO 7668, written mainly for clear anodize (ISO 7668); agree which method and geometry apply before anyone records a number. The numbers do not replace the samples, since instruments on a textured or curved part can disagree with the eye, but they give you something to check when a sample is lost, damaged or suspected of fading. Without them, a faded master silently moves the target.
How do you reference a golden sample on the drawing and purchase order?
Give every sample a unique number tied to the part number and drawing revision, and cite that number in a drawing note that names the surfaces it governs and the attribute it controls. A note that just says “match sample” does neither.
A workable drawing note reads like this:
FINISH: ANODIZE, COLOR BLACK. COLOR OF SURFACES MARKED A SHALL FALL BETWEEN APPROVED LIMIT SAMPLES LS-4410-01L (LIGHT) AND LS-4410-01D (DARK). TARGET PER MASTER SAMPLE MS-4410-01, REV C. SAMPLES GOVERN APPEARANCE ONLY; ALL DIMENSIONS AND COATING REQUIREMENTS PER THIS DRAWING.
The last sentence matters more than it looks. A physical sample has real dimensions, and if nothing says otherwise a supplier can reasonably argue that a part matching the golden sample is acceptable even when a feature on that sample is out of tolerance. The drawing should always win on anything it defines; the sample covers only what the drawing points it at.
On the purchase order, add a line that the samples listed on the drawing are part of the acceptance criteria and that the supplier holds a signed set. If the samples carry a revision letter, raise it with the drawing revision whenever an engineering change affects finish or appearance, so an old sample cannot be used to accept a new part. The guide on ballooned drawings and inspection reports shows how to give the appearance note its own balloon so it appears as a line item on the first article report.
Can a golden sample also be used to control fit?
Yes, as a functional reference part for assembly feel, snap or press behavior, or alignment with a mating part, but only alongside the dimensions and gauges that define the fit. A fit sample confirms the drawing works; it must not become the specification.
Fit samples are useful where the result depends on a combination of features: a cover that must sit flush with a housing, a knob that must turn with a particular drag, a bracket that has to align with a customer’s holes. Keep a matched pair, the supplier’s part and the mating part from your side, so the supplier can trial-assemble before shipping. When a fit sample and the drawing disagree, treat it as a drawing problem to be fixed by engineering change, not something to resolve by measuring the sample and copying it. For tolerances that decide the fit itself, see clearance, transition and interference fits.
How long does a golden sample stay valid, and who keeps it?
A golden sample stays valid while it still represents the approved condition, which means it needs controlled storage, a periodic check against its recorded readings or a sealed spare, and replacement when it is damaged, faded or superseded by a drawing change. Both buyer and supplier should hold a matched, signed set.
Store samples away from daylight, in sealed bags with the label outside, and do not use the master as a handling sample on the line. Dyed anodize can fade with light exposure, and powder coat and plated finishes pick up fingerprints and scratches from repeated handling. A simple routine is to keep a sealed spare of each sample that is opened only to check whether the working copy has drifted. When the comparison shows drift, or when a supplier changes the dye, the coating system or the base material, re-approve a new set from current production and retire the old one with a dated record.
Photographs help but do not substitute. Cameras, screens and printers all shift color, so a photo of a sample is useful for showing which defect a boundary sample represents, and weak for judging shade. Send photographs with a scale and the sample number in the frame, and keep the physical set as the deciding reference.
What should the RFQ say about samples, and how does Saola handle them?
Tell the supplier at quote stage which surfaces are governed by samples, who supplies the first golden sample, and how many sets you need, because samples change racking, handling and packing. Saola has parts finished to the cosmetic standard the buyer supplies and asks for one before production when none is given.
An RFQ for a part with an appearance requirement should list: the finish and its specification; the surfaces marked A or cosmetic; whether you will send an existing golden sample or want one built from the first lot; the attributes that need limit pairs; the viewing condition; how many signed sets each side holds; and whether you have instrument readings to share. The general list of what to send is in the guide on preparing a machining RFQ.
At Saola Manufacturing, anodizing on aluminum, powder coating and pad printing are part of the surface finishing menu our partner plants apply, along with electroplating, gold and zinc plating, blue trivalent chromate and oil-dip rust protection. The quality page states that parts are finished to the cosmetic standard the buyer supplies, whether a boundary sample, a written specification or marked-up photos, and that if no standard is supplied Saola asks for one before running production; the quote names where each finishing step is done. It also lists sample approval as a step of its own between first article and production, in which the buyer reviews the first article and any cosmetic samples and signs off. If you want instrument readings recorded on the samples, say so in the RFQ, or supply the readings from your own lab. Finishes outside the menu, such as decorative chrome-look plating, are not offered today. Send the drawing and sample requirements through the quote form.
Frequently asked
Is a golden sample the same as a first article?
No. A first article proves the process can make the part to the drawing and is documented by measurement. A golden sample is a reference for attributes the drawing does not fully define. The golden sample is often chosen from the first article lot, but it is a separate, separately signed object. See the guide on first article inspection with an overseas supplier.
Who should sign the samples?
Someone on the buyer side with authority over appearance, usually quality or design engineering, and the supplier’s quality lead. Signatures, date, sample number and drawing revision go on a tag or label attached to the part or its bag, and into a sample record held by both sides.
Do limit samples replace an AQL sampling plan?
No. The samples define what a defect is for appearance; the sampling plan defines how many parts are compared and how many failures a lot may contain. Both belong in the acceptance criteria. The guide on AQL sampling for machined parts covers the plan.
What if the supplier’s parts match the golden sample but my customer rejects them?
Then the sample set does not represent what the end customer accepts, and it needs to be rebuilt with the customer’s input. Until it is, the supplier has met the agreed standard. That is the reason to involve whoever makes the final appearance call before the samples are signed, not after.
Can one golden sample cover several part numbers with the same finish?
For color, often yes, if the parts share the alloy, finish and process. Shape, alloy and surface texture all change how a finish reads, so a cast housing and a machined bar part in the same black anodize usually need their own samples, and the drawing note should say which sample applies.
Sources
- Production Part Approval Process (PPAP), 4th edition, Automotive Industry Action Group, 2006
- ASTM D1729, Standard Practice for Visual Appraisal of Colors and Color Differences of Diffusely-Illuminated Opaque Materials, ASTM International, 2022 (D1729-22)
- ASTM D2244, Standard Practice for Calculation of Color Tolerances and Color Differences from Instrumentally Measured Color Coordinates, ASTM International, 2025 (D2244-25)
- ASTM D523, Standard Test Method for Specular Gloss, ASTM International, 2025 (D523-25; scope is nonmetallic specimens)
- ISO 3668:2017, Paints and varnishes — Visual comparison of the color of paints, International Organization for Standardization, 2017 (reviewed and confirmed 2022)
- ISO 7668:2021, Anodizing of aluminum and its alloys — Measurement of specular reflectance and specular gloss of anodic oxidation coatings, International Organization for Standardization, 2021