Projection Microscope Method
Optical microscopy methodology specified for the determination of wool fiber diameter defines the core procedure found in iwto 19 as applied to international trade samples. This standard, published by the international wool textile organisation, provides the reference method for measuring the fineness of wool fibers using a projection microscope. It is considered the most accurate way to verify the mean diameter and the distribution of widths in a lot of scoured or carded wool.
The test involves magnifying small snippets of the fiber and measuring them against a calibrated scale on a ground-glass screen. While automated methods like laserscan are faster, iwto 19 remains the definitive standard for settling disputes and for calibrating other testing equipment.
Sample Selection
Preparation of the fiber snippets is a critical step that must be performed according to the strict guidelines of the standard. To ensure a representative result, a large number of fibers must be sampled from different parts of the bale or the processing lot. The iwto 19 method requires the fibers to be cut into short sections, typically less than a millimeter in length, using a specialized cross-sectioning tool.
These snippets are then mounted on a glass slide using a mounting medium that has the correct refractive index to make the fiber edges clear and sharp. The mechanism of sampling ensures that every part of the lot has an equal chance of being measured, which minimizes the risk of bias in the final result. Technicians must be careful to avoid overlapping fibers on the slide, as this would make it impossible to measure the diameter of individual filaments accurately.
Measurement Accuracy
Measurements are conducted by a trained operator who identifies and measures the width of at least five hundred fibers per slide. Under the rules of iwto 19, the microscope must be calibrated using a standard scale to ensure that the magnification is correct and consistent across different laboratories. The operator moves the slide in a systematic pattern to avoid measuring the same fiber twice and to cover the entire area of the mount.
Each measurement is recorded, and the data is used to calculate the mean fiber diameter and the standard deviation of the lot. This manual process is highly sensitive to the skill of the operator, who must be able to distinguish between different types of fiber and to identify the true edges of the filaments. The boundary of the test is defined by the number of measurements required to achieve a specific level of statistical confidence in the result.
Trade Verification
Commercial transactions in the global wool market are often based on the test reports generated using this reference method. Adherence to iwto 19 allows buyers and sellers to have a common language for describing the quality of the fiber and for setting prices based on fineness. Because it is the international reference standard, the results are accepted by customs authorities, insurance companies and quality control agencies worldwide.
If two laboratories produce different results for the same lot, the projection microscope method is used to determine the correct value and to resolve the disagreement. Maintaining the equipment and the proficiency of the technicians is necessary for any laboratory that wishes to participate in the international trade of luxury fibers. Regular round robin tests are conducted between certified labs to ensure that the measurements remain harmonized across the industry.
