ISO 21575:2018 PDF

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