Overview
ISO 14368-3:2003 defines qualitative criteria and test methods for circular mineral and sapphire watch‑glasses used in horology. Part 3 of the ISO 14368 series specifies the nomenclature for defects (chips, scratches, waves, stains, greying, orange peel, bubbles, etc.), minimum physical and aesthetic requirements, and standardized procedures to verify mechanical and optical properties. The standard supports consistent quality control for watch‑glass production and inspection.
Key topics and requirements
- Defect nomenclature: Clear definitions for common faults - chip, scratch, wave effect, flaw, stain, greying, orange peel, deep defect (bubbles/crystallization), and vibrations - to harmonize inspection language.
- Hardness testing: Preferred Knoop imprint method (alternative: Vickers). Measurements are taken at 1 N load to reduce variability from surface treatments. Table 1 gives hardness ranges (e.g., sapphire ~1 800–2 200 HK 0.1).
- Breakage (ball‑impact) energy: Ball‑drop test using a 25 mm steel ball (0.635 N weight) released from increasing heights. Breakage energy is calculated as weight × drop height. Specified ranges for mineral and sapphire glasses (for 1 mm thickness and 22–30 mm diameter) are provided in the standard.
- Static load test: Determines reinforcement/hardening by applying a 300 N load to a 3.175 mm steel ball placed centrally on the glass supported over a rubber pad; no damage indicates reinforcement.
- Surface stress measurement: Uses commercial optical polariscopes to measure surface compressive stress and depth of stress layer; acceptance based on specified application values.
- Visual inspection: Annex A recommends inspection at 30 cm in a controlled dark workstation with 1 500 lx vertical/horizontal lighting; acceptance for some defects remains subjective and agreed between supplier and customer.
Applications and who uses it
ISO 14368-3 is primarily used by:
- Watch manufacturers and suppliers of mineral and sapphire crystals
- Quality control and inspection engineers in watchmaking
- Contract manufacturers, case and crystal designers, and laboratory testers
- Standards and compliance teams in horology
Practical applications include incoming inspection of watch‑glasses, production QC, supplier agreements on acceptance criteria, and failure analysis of cracked or flawed crystals.
Related standards
- ISO 14368-1:2000 - Dimensions and tolerances for mineral and sapphire watch‑glasses
- ISO 14368-2 - Assembly to the case by adhesive or gasket
- ISO 286 series - System of limits and fits (referenced for terms and tolerances)
Keywords: ISO 14368-3, mineral watch-glasses, sapphire watch-glasses, qualitative criteria, test methods, watch glass defects, hardness test, ball impact test, surface stress, watchmaking quality control.