A semi-finished blank order needs more than a base-curve number. Confirm the supplier's curve convention, material, design, diameter, thickness and intended surfacing system. The receiving laboratory should approve how the blank will be used for the target jobs. A number copied from an old purchase order is not enough to establish compatibility with a new blank family.
Key takeaways
- Ask how the supplier defines and measures its base-curve label.
- Approve the blank family with the laboratory that will surface it.
- Keep design and geometry revisions attached to the SKU.
Why a base-curve label needs context
In a semi-finished supply program, one surface is supplied for subsequent prescription processing. ZEISS describes the distinction between stock production and individualized prescription manufacturing. The purchasing question is whether the supplied blank and the laboratory's process work together for the intended design.
Ask for the manufacturer's specification sheet rather than assuming two similarly labeled curves are interchangeable. Where physical geometry matters, request the relevant radius or sag information and its measurement convention from the supplier.
Reference: ZEISS: How spectacle lenses are manufactured
Build a blank-family approval sheet
Have procurement and the laboratory review the same sheet. Commercial availability should not be treated as technical approval, and a successful laboratory trial should not be treated as confirmation of every commercial quantity.
| Specification | Confirmation to request | Reviewer |
|---|---|---|
| Curve and design | Curve convention, design identifier and revision | Laboratory technical team |
| Blank geometry | Diameter, thickness and usable processing area | Surfacing team |
| Material | Exact material identification and processing instructions | Process owner |
| Range | Approved job range and excluded combinations | Laboratory plus purchasing |
Plan a representative surfacing trial
Choose trial jobs that exercise the intended range rather than only one convenient prescription. Ask the laboratory to select cases representing its normal processing conditions and the more demanding edges of the proposed range. Record the blank batch, job inputs, software or design version where relevant, and finished inspection results.
If one case fails, investigate its cause before rejecting or accepting the entire family. A setup error, an unsuitable blank choice and a material issue require different responses. Keep the trial record specific enough that another operator can repeat the assessment.
- Identify the exact blank used for each trial.
- Record equipment and process settings under the laboratory's procedures.
- Document optical, dimensional and cosmetic acceptance separately.
- Approve only the combinations actually covered by the trial and technical review.
Control changes after approval
Require notification when a supplier proposes a different material, curve family, mold design or blank geometry. Use a separate item revision where the change affects processing. The warehouse should be able to keep old and new versions apart until the laboratory authorizes their use.
For repeat orders, include the approved specification reference and packaging identification. This is more reliable than a short description such as 'same base as last time,' especially when staff or suppliers change.
Buyer questions
Frequently asked questions
Is a base-curve number a complete blank specification?
No. Material, design, geometry, measurement convention and laboratory compatibility must also be confirmed.
Can two suppliers' blanks with the same curve label be substituted?
Only after the receiving laboratory reviews the specifications and approves the relevant processing trial.
Who should choose the blank for an RX job?
The laboratory's qualified technical team should select it using the design requirements, job data and validated production process.
Further reading
These external references provide background context. Product availability and performance claims must still be confirmed for the exact item being purchased.