An anti reflective sapphire crystal coating brief is complete only when it defines reflectance targets per surface, which side carries the coating, the wavelength band the coating must cover, and the test methods used to verify adhesion, abrasion and visual colour. Most first briefs stop at "AR coating, clear finish" — and that gap is where re-quotes begin.
Why first briefs fall short
When a sourcing team writes to a sapphire component manufacturer, the brief tends to describe the outcome they want: low glare, no obvious tint, durable surface. Those are goals, not specifications. A supplier receiving goals rather than measurements can still quote — but the quote will rest on assumptions, and every assumption is a future clarification round.
The measurements buyers omit fall into a predictable pattern. They are the ones that sit between the optical result the brand wants and the physical process that delivers it: which face is coated, how reflectance is quantified, over which wavelengths, and how durability is tested. None of these are exotic. They are simply not the first things a buyer thinks to write down.
A structured review before the brief is sent closes that gap. The framework below is one way to do it.
The Coating Specification Gate (CSG)
The Coating Specification Gate is a three-pass review you apply to your own brief before it reaches a supplier. Each pass catches a different class of omission.
Pass 1 — Optical measurements. Define reflectance as a target per coated surface, and state the wavelength range the target applies to. Decide whether one side or both sides are coated, and document that decision. Define acceptable reflected colour appearance in observable terms, so tint disputes are settled against an agreed reference, not opinion.
Pass 2 — Mechanical and environmental verification. Name the adhesion and abrasion test methods you will accept, and the environmental conditions the coating must withstand in your product's intended use. Decide whether the coating must survive assembly processes downstream — and say so.
Pass 3 — Documentation and approval. Specify what evidence the supplier must provide: measurement reports for reflectance, test records for adhesion and abrasion, and inspection criteria for visual defects. Agree in writing which party approves each measurement, and at what stage a failure stops production rather than being noted.
Each pass is a gate in the literal sense: if your brief cannot answer a pass, you are not ready to quote, and the honest move is to ask the supplier to help you close the gap — with their recommendations documented in the specification, not assumed.
Decision table: coating configuration choices
| Decision | Options to compare | What to verify with the supplier | What to document in the brief |
|---|---|---|---|
| Coated side(s) | Outer only; inner only; both sides | Effect of each option on reflectance, coating exposure to wear, and cost implications — confirm current pricing policy directly | The exact coated face(s), stated explicitly |
| Reflectance target | A defined value per coated surface, over a stated band | Which band the supplier designs and measures against | The target value, the band, and the measurement method |
| Coating construction | Number of layers and design approach | What the supplier recommends for the application and why | The agreed construction reference or drawing note |
| Colour appearance | Neutral target vs slight residual tint | How the supplier controls and inspects reflected colour | An agreed visual reference or measured colour criterion |
| Durability verification | Named adhesion, abrasion and environmental test methods | Which methods the supplier can run and report | The test names, acceptance criteria and report format |
| Inspection scope | Sampling approach for coating defects | What inspection the supplier performs and records | Sampling plan and defect acceptance criteria |
Note that no option above carries a default recommendation. The right configuration depends on the watch design, the market, and the assembly process — which is why the brief must state choices rather than leave them implied.
Approval questions to put to the supplier
Before you approve a coating specification, put these questions directly to the manufacturer and record the answers in the spec:
- What reflectance value per coated surface can you commit to, measured over which wavelength band, and with which instrument and method?
- What adhesion and abrasion test methods do you run on AR coatings, and what are the pass criteria you will report against?
- How do you control and inspect reflected colour, and can we agree a visual reference sample before production?
- For a two-side coating, what protection does the inner coating have during case assembly, and what handling requirements should our assembly line follow?
- What measurement reports, test records and inspection documentation will accompany each delivery?
- What is your current policy on samples, and what are the terms we should confirm before requesting them?
That last question matters. Sample terms, fees, shipping arrangements and production policies are project-specific and change over time. Nothing in this article should be read as describing them; confirm the current position directly before it becomes part of your plan.
What to hold constant, what to leave open
A good brief is firm on measurements and open on method. The reflectance target, coated faces, test methods and acceptance criteria should be locked before quoting. The layer construction, deposition process details and internal process controls can stay open — they are the supplier's domain, and dictating them adds no protection that verification would not add better.
This division also protects you during engineering changes. If a measurement fails, the conversation is about the measurement, not about whose process preference was overridden.
FAQ
Does an anti reflective coating change the dimensional spec of the sapphire crystal? A coating adds a thin film to the coated surfaces. Whether your part tolerances need to account for that is a drawing-level question — confirm with the supplier how coating thickness is treated relative to your stated dimensions, and document the answer.
Should the outer face be coated at all? Outer-face coating improves glare performance but exposes the coating to wear. Inner-only coating protects the film at some optical cost. Neither choice is universally correct; the decision belongs in the brief, informed by the product's use and the supplier's input.
How do I judge a supplier's coating quality without visiting the plant? Ask for documented measurement: reflectance reports against your stated band, adhesion and abrasion test records with named methods, and inspection criteria for visual defects. A supplier who can describe these fluently and commit to them in writing is demonstrating capability in the way that matters at a distance.
Can we start with a simpler spec and refine later? You can, but each refinement after quoting risks a re-quote and schedule impact. The CSG review costs an hour; a missing measurement discovered after tooling costs far more. Start with the gate.
What if we don't know which reflectance target to choose? Say so, and ask the supplier to propose options with their measurement basis. What you should still document is the method and band the target will be measured against — that stays fixed even while the value is being decided.
Next steps
Primary action: confirm a coating specification with JadeZone Sapphire. Send your crystal drawing with the CSG answers — coated faces, reflectance target and band, test methods, acceptance criteria and documentation requirements — and we will review the specification with you before any quotation proceeds.
Low-friction option: not ready to write the full brief? Download our mental checklist below and confirm your own answers first:
- Coated face(s) stated explicitly
- Reflectance target defined per surface, with wavelength band
- Reflected colour criterion agreed
- Adhesion and abrasion test methods named
- Environmental exposure requirements stated
- Inspection and reporting scope agreed in writing
- Sample and production policies confirmed directly with the supplier