ISO 21575:2018

Overview

ISO 21575:2018 - Optics and photonics - The powder test method for the water resistance of optical glass - specifies the general procedures for evaluating the water resistance of optical glass using the powder test method. The standard defines specimen preparation, required apparatus, reagents, test procedure and classification by percentage weight loss after boiling in water. The powder method is an alternative to the surface method and is noted for simpler sample preparation because it does not require polished surfaces.

Key topics and technical requirements

• Specimen preparation

  • Grind glass and sieve to collect particle sizes between 425 µm and 600 µm.
  • Wash/de-dust by repeated decantation with pure alcohol, then dry at 120–130 °C and store in a desiccator.
  • Sample mass: use a powder mass equivalent to the glass specific gravity (grams) in the test basket and use ~3× specific gravity for initial decantation steps.

• Reagents and water quality

  • Water must meet ISO 3696 Grade 2 (analytical laboratory water).
  • Alcohols allowed: ethanol, methanol, 2‑propanol (no water-containing alcohol).

• Apparatus

  • Test sieves per ISO 3310‑1.
  • Platinum mesh basket for corrosion test: opening 230–260 µm, wire diameter ≈ 76 µm.
  • Flask and condenser conforming to ISO 4797 / ISO 4799; nominal spherical flask capacity 100 ml.
  • Heating water bath maintaining temperature > 98 °C (measured 20 mm ± 10 mm from flask bottom).

• Test procedure

  • Place powdered specimen in platinum basket, weigh, boil in 80 ml pure water for 60 minutes, rinse with alcohol, dry (120–130 °C), cool in desiccator and weigh.
  • Repeat the full procedure twice; calculate percentage weight loss from initial mass and report mean of two measurements.

• Classification

  • Water resistance classes 1 to 6 based on percentage weight loss. (Class thresholds per Table 1 in ISO 21575:2018: e.g., Class 1 <0.05%, Class 2 <0.10%, Class 3 <0.25%, Class 4 <0.60%, Class 5 <1.10%, Class 6 ≥1.10%.)

Applications and users

• Intended for optical glass manufacturers, quality control and test laboratories, materials scientists, and photonics component producers.
• Practical uses:
  • Material selection and specification for lenses, prisms, windows and optical components exposed to moisture or humid environments.
  • Quality control, acceptance testing and comparative assessment of chemical durability among glass batches.
  • R&D for new optical glass formulations where water resistance is a performance parameter.

Related standards

• ISO 3310‑1 (Test sieves)
• ISO 3696 (Water for analytical laboratory use)
• ISO 4797, ISO 4799 (Laboratory glassware - boiling flasks and condensers)

Keywords: ISO 21575:2018, powder test method, water resistance, optical glass, optics and photonics, optical materials, weight loss classification, platinum basket, test procedure.