Overview
ISO 137:2015 - "Wool - Determination of fibre diameter - Projection microscope method" specifies a standardized laboratory procedure for measuring wool fibre diameter by projecting magnified fibre snippets onto a screen and reading their projected widths. The method is suitable for wool in any form and for other fibres with reasonably circular cross-sections. ISO 137:2015 updates the earlier 1975 edition and is based on IWTO-8:2011.
Key topics and technical requirements
- Principle: measure the projected width of fibre snippets using a projection microscope to obtain the mean diameter.
- Apparatus: projection microscope with light source, condenser, stage, objective/ocular capable of 500× magnification, circular screen with graduated scale; certified micrometer scale for calibration (0.01 mm on stage projects to 5 mm on screen).
- Stage movement: sliding stage with 1.0 mm step capability to ensure random, non-overlapping fields.
- Snippet cutting: cut fibre pieces of 0.8 mm length using a fibre holder/pusher or a microtome; detailed cutter designs and procedures are specified to avoid selection bias.
- Mounting medium: refractive index 1.43–1.53 at 20 °C, suitable viscosity, zero water absorption, and no effect on fibre diameter (examples: cedarwood oil, liquid paraffin; anhydrous glycerine not suitable).
- Sampling & conditioning: total sample preparation follows ISO 1130; conditioning in the standard atmosphere per ISO 139.
- Measurement rules: traverse slide in 1.0 mm steps, measure every fibre image in the measurement area except those excluded by defined criteria (e.g., partly outside central circle, damaged, overlapping).
- Calibration, calculation & reporting: magnification checks, periodic calibration with micrometer scale, calculation of mean diameter, and reporting requirements; annexes provide example calculations and confidence limits.
Applications and users
ISO 137:2015 is used for:
- Textile and wool testing laboratories for quality control and specification verification.
- Wool brokers and processors for grading and batch assessment during scouring, carding or spinning stages.
- Yarn and fabric manufacturers monitoring raw fibre properties to optimize processing.
- Research and development in fibre science and textile engineering.
- Instrument manufacturers and calibration labs for verifying projection microscope performance.
This method provides a direct, reproducible measure of wool fibre diameter, supporting product grading, process control, material selection and compliance with textile quality standards.
Related standards
- ISO 139 - Textiles - Standard atmospheres for conditioning and testing
- ISO 1130 - Textile fibres - Some methods of sampling for testing
- IWTO-8:2011 - Source method referenced in the development of ISO 137:2015
Keywords: ISO 137, wool fibre diameter, projection microscope method, fibre diameter testing, textile testing standard, wool measurement.
