Overview
ISO 10629:1996 specifies a standardized test method and classification for the resistance of raw optical glass to attack by aqueous alkaline solutions at 50 °C. The method measures mass loss and surface changes after exposure to a sodium hydroxide test solution and calculates the time required to etch a surface layer to a depth of 0.1 µm. Results are used to assign an alkali resistance (AR) class for optical glass.
Key topics and technical requirements
- Test solution and conditions
- Sodium hydroxide-based test solution (prepared from a 0.1 mol/l NaOH stock, diluted to the required concentration); pH controlled (carbonate-free) and held at 50.0 °C ± 0.2 °C.
- Sample preparation
- Typical sample dimensions: nominally 30 mm × 30 mm × 2 mm (annealed) with defined fine grinding and polishing procedures (cerium oxide polishing; control of rotation speeds, pressure and polishing time).
- Apparatus and handling
- Stainless-steel cylindrical test vessel with stirrer, thermostatic heating bath, analytical balance (±0.1 mg), ultrasonic cleaning, pH electrode, and inert sample supports (platinum/silver wires or cages).
- Test procedure
- Immersion sequences for unknown and known glasses (common exposure intervals: 0.25 h, 1 h, 4 h, 16 h), stirring at specified rates, single-use samples, and defined cleaning/drying protocol (ultrasonic cleaning, nitric acid rinse to pH 4.5, 2‑propanol).
- Measurement and calculation
- Determine mass loss (m1 − m2), measure density and surface area, then compute the time to etch 0.1 µm using the formula given in clause 8. Classification is based on computed time ranges.
- Surface change notation
- In addition to AR class, surface observations are recorded using codes (e.g., 0: no visible change; .1: pitting/waviness; .2: staining/interference colours; .3: tenacious whitish layer; .4: loose thick deposit/strong attack).
- Test report
- Must include reference to ISO 10629, sample ID and density, tested surface area, attack time used for calculation, number of samples, AR designation and any unusual observations.
Applications and users
- Intended for manufacturers of optical glass, quality-control and testing laboratories, R&D teams, suppliers, and purchasers of raw optical glass.
- Practical uses:
- Specifying glass grades for lenses, prisms and optical components where chemical durability matters.
- Comparing batches or formulations for alkali resistance.
- Supporting material selection in optical instrument manufacturing and in environments where alkaline exposure is a concern.
Related standards
Keywords: ISO 10629:1996, raw optical glass, alkali resistance, test method, classification, sodium hydroxide, 50 °C, etch depth, mass loss, optical glass testing.
Open preview (PDF)Raw optical glass — Resistance to attack by aqueous alkaline solutions at 50 degrees C — Test method and classification