Overview
EN ISO 137:2015 / ISO 137:2015 specifies the procedure and measurement conditions for determining wool fibre diameter using the projection microscope method. Adopted by CEN as EN ISO 137:2015, the standard describes how to project magnified images of fibre snippets onto a screen and measure their projected widths to obtain mean diameter values. The method is suitable for wool in any form and for other fibres with reasonably circular cross-sections. Note: dyed, bleached or finished fibres can give different diameters than untreated fibres, and measurements at different processing stages may vary.
Key topics and requirements
- Principle: Projected images of fibre snippets are measured on a graduated screen to determine the projected width (mean diameter).
- Apparatus:
- Projection microscope with light source, condenser, movable stage and circular screen.
- Objective/ocular combination capable of 500× magnification (calibrated by a certified micrometer).
- Micrometer graduated scale for periodic calibration (0.01 mm divisions projected to cover 5 mm on screen for 500×).
- Snippet cutters or microtome and fibre holder/pusher for controlled snippet length.
- Mounting medium with refractive index between 1.43 and 1.53 (e.g., cedarwood oil, liquid paraffin); anhydrous glycerine is not suitable.
- Standard microscope slides and No. 1 cover glasses.
- Sampling & specimen prep: Total sample and subsample preparation follow ISO 1130 and conditioning per ISO 139 where applicable. Procedures for raw wool, slivers/rovings/yarns, snippet cutting and mounting are described.
- Measurement procedure: Randomized sampling of fibres, focusing, measuring projected widths within an optically reliable area of the screen, recording measurements and calculating mean diameter.
- Reporting & accuracy: Calculation rules, example calculations (Annex A), and confidence limits/accuracy guidance (Annex B) are included.
Applications and users
Applications of EN ISO 137:2015 include:
- Quality control and grading of wool by fibre diameter.
- Textile manufacturing and yarn production where fibre diameter affects spinning, fabric handle and end-product performance.
- Research & development in fibre science and textile laboratories monitoring processing effects (dyeing, finishing).
- Standards bodies and certification labs performing compliant fibre measurements for specifications and trade.
Typical users: wool testing laboratories, textile mills, research institutes, spinners, raw wool brokers and quality assurance teams.
Related standards
- ISO 139 - Standard atmospheres for conditioning and testing
- ISO 1130 - Sampling methods for textile fibres
- IWTO-8:2011 - Method basis referenced in ISO 137 development
- CEN adoption: EN ISO 137:2015
Keywords: wool fibre diameter, projection microscope method, EN ISO 137:2015, ISO 137:2015, wool testing, fibre diameter determination, projection microscope calibration.
