ISO 22531:2020

Overview

ISO 22531:2020 specifies a laboratory test method for the climate resistance of optical glass and the procedure for classifying glass based on the results. It defines the test setup, specimen preparation, temperature cycling, measurement of optical degradation (haze) and the calculation method used to quantify change in optical quality after exposure to a controlled humid/thermal environment.

Key topics and technical requirements

• Test principle: Measure haze of polished optical-glass specimens before and after a controlled temperature/humidity cycling; climate resistance is determined by the change in haze.
• Specimens: Square plates 30 mm × 30 mm × 3 mm; 5 to 8 specimens per test. Surfaces polished with cerium oxide slurry and cleaned (organic solvent, detergent, distilled water, alcohol such as IPA). Immediate testing within defined exposure/storage windows is required.
• Test apparatus:
  • Glass water tank (borosilicate per ISO 3585 or quartz, 5–20 mm thickness) inside a thermostatic chamber.
  • Stirring unit with stirring rod and fan; stirring fan rotated at 100 r/min. Seal (e.g., O‑ring) to maintain humidity.
  • Water purity: ISO 3696 grade 2, volume 1.8 L.
  • Thermostatic chamber with automatic temperature control and a through‑hole for the stirring rod.
• Temperature profile and timing:
  • Maintain air in tank at 57.5 °C (tolerance ±0.5 °C) and hold for 50 minutes, then apply cyclic profile so tank air cycles between 57.5 °C and 64.0 °C.
  • Cycle duration as specified in Annex A and total exposure of 48 hours.
• Measurement and calculation:
  • Haze measured using a haze meter per ISO 14782 (measurements >5 mm from specimen edge).
  • Change in haze ΔH(k) computed per specimen; exclude the single maximum and minimum ΔH values, then average remaining values to obtain the reported ΔHave for classification.

Applications and who uses it

• Manufacturers and quality engineers of optical components (lenses, prisms, windows) who need to validate long‑term optical performance under humid thermal stress.
• R&D teams developing new optical glass formulations or coatings for harsh environments.
• Test labs and certification bodies performing environmental durability testing for optics and photonics products.
• Product managers and procurement teams specifying climate‑resistance requirements in supplier contracts.

Related standards

• ISO 14782 - Haze measurement for transparent materials (required measurement method)
• ISO 3585 - Borosilicate glass 3.3 - Properties (tank material)
• ISO 3696 - Water for analytical laboratory use - Specification and test methods

Keywords: ISO 22531:2020, climate resistance, optical glass, haze, haze meter, optics and photonics, test method, environmental testing, glass water tank, thermostatic chamber.