When buyers brief an anti reflective sapphire crystal coating, the most frequently missed measurements are: which surfaces are coated (outer, inner, or both), the target reflectance per coated surface, the wavelength band and measurement geometry used to verify it, and the adhesion and abrasion acceptance criteria applied to coated edges and bevels. Without these, supplier quotations describe different products. A workable first brief answers the Four-Surface Question and states how reflectance will be measured and approved.
The Four-Surface Question framework
Before discussing coating materials, answer four questions in order:
- Inner surface — will it be coated? Inner-only coating protects the coating from abrasion during wear and polishing during service.
- Outer surface — will it be coated? Outer coating reduces front-face glare but is exposed to abrasion and cleaning.
- Bevel and edge — will coating wrap the chamfer, stop before it, or be masked? Edge coverage is where adhesion complaints originate.
- Verification surface — how will reflectance be measured: on the flat, across the curve, per side or assembled?
This framework does not tell you which configuration is correct. It forces each configuration decision to be explicit so that quotations, samples and approvals can be compared like for like.
Measurements and decisions to put in the first brief
| Brief element | Why it matters | What to specify or ask |
|---|---|---|
| Coated surfaces (inner / outer / both) | Determines glare reduction, abrasion exposure and service behaviour | State sides explicitly; ask how each side is verified |
| Target reflectance per coated surface | "Low reflection" is not a specification | Give a target value and the wavelength band it applies to |
| Measurement geometry | Reflectance readings depend on angle and band | Ask what instrument, angle and band the supplier measures with |
| Colour/tint appearance | Tint is a visible by-product, not a performance figure | Ask for tint descriptors and whether tint can be adjusted |
| Coating stack configuration (single-layer vs multi-layer) | Affects achievable reflectance and cost structure | Ask which stack the supplier proposes for your target and why |
| Bevel and edge treatment | Adhesion failures cluster at edges | Ask whether coating covers, stops at, or is masked from the bevel |
| Adhesion and abrasion acceptance criteria | Defines pass/fail for the coating, not the substrate | Ask which adhesion and abrasion tests the supplier runs and what constitutes a pass |
| Measurement documentation | Evidence for incoming inspection and dispute resolution | Ask whether measurement reports accompany batches |
| Assembly compatibility | Coating can interact with gaskets, adhesives and printing | Ask about compatibility with your gasket and adhesive materials |
| Service and re-polishing behaviour | Determines aftermarket repair options | Ask whether outer coating can be polished or must be stripped and re-coated |
Treat every row above as a question to document in writing, not an assumption. Where the supplier's answer differs from your assumption, that difference is exactly the gap the first brief should close.
Concrete approval questions
Put these to the coating supplier before approving a specification:
- Which surfaces does this quotation assume are coated — inner, outer, both, or both plus bevel?
- What reflectance figure does the quotation target, over which wavelength band, and at what measurement angle?
- Which instrument and reference method will be used, and will a measurement report accompany the approval sample?
- What adhesion and abrasion tests are proposed, and what is the documented pass criterion?
- How is the bevel treated in coating and in masking?
- Is the coating stack single-layer or multi-layer, and what does that choice trade off?
- How does the coating behave with our gasket, adhesive and dial-printing materials?
- If the outer coating is scratched in service, what repair route applies — polishing, stripping, or replacement?
- Confirm the current policy directly for samples, fees and shipping arrangements.
- Confirm the current policy directly for minimum order quantity, lead time and pricing.
Questions nine and ten are deliberate placeholders. They exist so the brief template forces a direct, current-answer conversation instead of a recall of assumptions.
What the first brief should sound like
A defensible coating brief reads something like this: "Sapphire crystal, flat top with chamfer; inner surface coated, outer surface uncoated; target reflectance and measurement band to be agreed with supplier; bevel masked; adhesion and abrasion acceptance criteria per supplier's proposed test method, documented in the approval report." Notice that it names decisions rather than adjectives. Every adjective left in a brief becomes an interpretation the supplier makes on your behalf.
FAQ
Does coating both sides always make sense? Not automatically. Coating both sides maximises glare reduction but exposes the outer coating to abrasion and changes the service story. Many buyers choose inner-only coating for watches expected to be polished during service. Decide per product, per wearer profile, and document the choice.
Is a blue tint a defect? A tint is a visible consequence of the coating stack's reflectance curve. Whether it is acceptable is a brand decision, not a technical defect category. Agree tint descriptors and reflectance targets together so the supplier optimises for your intended appearance.
What is the single most useful document to request? A measurement report tied to the approval sample, showing reflectance per coated surface under the agreed geometry and band. It converts "looks good" into a repeatable incoming-inspection reference.
How do I compare suppliers fairly? Send the identical Four-Surface Question brief to each supplier and compare their answers line by line. Differences in assumed coated surfaces, measurement method or acceptance criteria explain most apparent price and quality gaps between quotes.
Who should sign off the coating specification? The sourcing manager should own the document, with sign-off from the product developer for appearance and from the service or aftermarket function for repairability. A coating choice is a lifecycle decision, not only a purchasing one.
Confirm a coating specification
If you are preparing a brief for an anti reflective sapphire crystal coating, JadeZone Sapphire can review your draft specification against our coating process and flag the measurements that need to be fixed before quoting. Send your crystal drawing, your Four-Surface Question answers and your reflectance intent, and we will confirm a coating specification together. Confirm the current policy directly for samples, pricing and production terms.
Low-friction checklist CTA
Not ready to send a drawing? Use the ten approval questions above as a one-page checklist. Tick each answer in writing before your next supplier call — the checklist itself is the deliverable, and it costs nothing to run.