Wool Biology and Metrology

Revised Version

The original version of this module, released in 2008, included 18 topics.

This revised version, released in 2012, has been subject to a number of minor amendments, mostly related to formatting. The first 5 topics have had some additional text added, but they are substantially the same as the 2008 version.

Associated PPT files can be downloaded as a compressed archives:



Topic 01: Skin Structure and Function

The investigation of the biological mechanisms operating in mammalian skin has been hampered by the fact that the epidermis is very thin and contains cells at different stages of maturation and also hair follicles are very small. However, the past three decades have seen the development of many microscopic and biochemical techniques that enable molecular information to be obtained from small amounts of tissues. Our knowledge of the activities of skin structures has grown enormously. Sheep, mice and humans are the species mainly used by biologists as experimental models and the findings generally apply to the general knowledge of the activity of mammalian skin.

On completion of this topic you should have:

  • an understanding of the development of wool follicles in the skin
  • the knowledge of cellular and molecular mechanisms involved in the formation and activity of mature follicles growing wool
  • an appreciation of where our knowledge of wool growth is limited.

Topic 02: Structure and Composition of Wool

Wool is sheephair and belongs to the group of hard mammalian structures that include nails, claws and hooves. These structures are tissues and their cells are differentiated from epithelial cells and contain proteins that are called keratins.

Our knowledge of the chemical make-up of mammalian keratin originally came from extensive research carried out on wool in several countries but mainly in the UK, USA, Germany and Australia from about the late 1930’s to the end of the 1980’s. By the 1980’s research publications began to decrease as wool lost it’s dominant position in the textile fibre market and basic research gradually diminished. Currently fundamental research is still going on but with a marked orientation to commercial outcomes aimed at maintaining wool in the fibre market. An important change that has occurred in the last 20 years is the application of wool knowledge to research on the structure and mechanisms of growth of human hair in order to understand and treat diseases of hair as well as develop new products for the cosmetic/social role that hair plays.

On completion of this topic you should have:

  • An understanding of the range of proteins that can be extracted from wool
  • A knowledge of how the proteins are obtained and their amino acid composition sequences
  • A brief view of the organization of the gene families in human chromosomes
  • Knowledge of where the proteins are located in the fibre
  • An appreciation of the three-dimensional structure of intermediate filament proteins in general and the several higher orders of organization into keratin intermediate filaments (IFs).
  • Understanding of the relationships of keratin IFs and the matrix proteins
  • Knowledge of the disulphide and isopeptide bonds, some of their properties and where they are found in the fibre and follicle
  • An overview of the properties of wool in relation to its protein structure.

Topic 03: Follicle Kinetics

The hair or wool of mammals is the fully keratinised product of events occurring within the hair (wool) follicle and once this differentiation event has taken place, the keratinised fibre is no longer metabolically active. The hair (or wool) follicle on the other hand is one of the most highly metabolically active structures in the mammalian body plan and undergoes some of the most dramatic physical changes, not only, during initiation and morphogenesis in embryonic skin, but also throughout the functional lifetime of the follicle as it rotates through the phases of the hair cycle (anagen, catagen and telogen). This morphological pattern of change is generally the same for all follicles with the major difference being the temporal pattern, which varies with species, age, gender, spatial distribution and metabolic status of the animal.

On completion of this topic, you should be able to:

  • Describe the techniques that are routinely used to measure cell kinetics, wool growth rates and wool quality
  • Explain the application and limitations of each technique
  • Outline the basic biochemical and molecular mechanisms underpinning wool growth rates in the mature wool follicle
  • Critically assess scientific papers and related professional literature on factors influencing wool growth and fleece quality and the methods used to quantify the responses.

Topic 04: Genetic Engineering

This aim of this topic is to explain what is currently known about genes that are active in the adult wool follicle and to discuss the way that the process of genetic engineering can be used to cause the wool follicle to produce new wool fibre types. A detailed example of the first work done to achieve this will be given along with a description of the results and the potential of this technology for the future.

On completion of this topic you should have an understanding of:

  • The opportunity that transgenesis presents for the modification of wool properties
  • The method used to make transgenic sheep and results from early experiments
  • The genes that can be used as transgenes
  • The potential wool fibre modifications that could be made by transgenesis
  • The issues of biosafety, ethics and acceptance in relation to the use of transgenesis in sheep.

Topic 05: Background to Wool Metrology

Put quite simply, metrology is the science of measurement. In broad terms metrologists are generally focussed upon developing (evaluating) technologies and systems for objectively measuring the quality attributes of raw materials and manufactured products. This general definition applies as much to wool as to any other material.

By the end of this topic, you should have:

  • some knowledge of the history of wool metrology
  • an understanding of the essential technical requirements of wool measurement systems
  • an understanding of the sources of variation within wool metrology systems
  • knowledge of the procedures by which metrology standards are developed, including the role of IWTO, and
  • knowledge of the procedures whereby the technical limitations of metrology systems is managed.

Topic 06: Measurement Principles

Wool is a very variable material – it varies fibre to fibre, staple to staple, fleece to fleece, etc. Topic 1 – Background to Wool Metrology explains why this variation occurs. In order for measurements to have any meaning in terms of their representing the average properties of the lot of wool, it is necessary to have some understanding of the sources of variation and how they are described. This topic introduces some common statistical terms used in the description of variation, together with the more common techniques used to evaluate the effects of variation and thereby produce relatively robust sampling and measurement methods.

On completion of this topic you should have an understanding of:

  • the meaning of common statistical terms used in wool metrology
  • the effects of sources of variation on measurement techniques
  • the development of standard test methods.

Topic 07: Sampling Techniques

This topic describes the techniques involved in obtaining samples from bales of wool. Samples are taken prior to wool being sold, generally using mechanical apparatus. Two types of samples are taken. Grab samples that are further sub sampled and tested to determine average staple length and strength and then go on to serve as samples for inspection by buyers. Core samples are taken and tested to determine yield and mean fibre diameter.

By the end of this lecture, you should be able to:

  • Describe the reason grab and core samples are taken from wool bales
  • Describe the equipment used for grab and core sampling wool bales
  • Describe the key elements of the IWTO Test Methods for grab and core sampling wool bales
  • Describe the procedure used to grab and core sample wool bales
  • Understand the sampling factors that influence the precision of wool test results.

Topic 08: Yield

Presale testing for Yield has been an integral part of the Australian wool selling system since the introduction of Sale by Sample in July, 1972. Today virtually all Australian wool is tested for Yield (and Mean Fibre Diameter), irrespective of the method of marketing, and is sold to the processor on test results. In fact, failure to provide presale test information results in reduced competition and in severe price penalties.

By the end of this topic, you should have:

  • an understanding of the importance of Yield to the textile manufacturer
  • an understanding of the processes involved in producing an estimate for Yield
  • knowledge of the components which lead to estimates of Yield
  • knowledge of the different types of Yield estimates available, and the markets in which they most commonly apply, and
  • an understanding of the requirements in providing an estimate of Yield on an IWTO Test Certificate.

Topic 09: Fibre Diameter

As well as describing the measurement of Fibre Diameter of wool samples this topic briefly outlines the relevance of Fibre Diameter testing to the determination of wool value and to processing performance and quality of the textile or apparel end product. The differences between visual appraisal and measurement of Fibre Diameter are discussed, along with the sources of variation in Fibre Diameter testing. The relevance and measurement of CVD are outlined. The strengths and weaknesses of the four (4) main techniques of measurement, Projection Microscope, Airflow, Laserscan and OFDA100 are analysed. The distinction is made between the different forms of wool which are commonly tested commercially for Fibre Diameter, i.e. fleece samples, core samples of Sale Lots and wool top.

By the end of this topic, you should have an understanding of:

  • the relevance of Fibre Diameter to wool fibre value, processing performance and end product quality
  • the difference between visual appraisal and measurement of Fibre Diameter
  • the measurement of Mean and Coefficient of Variation of Fibre Diameter (CVD)
  • the sources of variation in Fibre Diameter measurement
  • sampling and sample preparation for the four (4) Standard methods of Fibre Diameter measurement, viz. Projection Microscope, Airflow, Laserscan and OFDA 100
  • Fibre Diameter testing of top, core and fleece samples (including On-farm Testing).

Topic 10: Staple Length, Staple Strength and Position of Break

This topic describes the subjective assessment and objective measurement of Staple Length, Staple Strength and Position of Break. The principles of the measurements made on an ATLAS instrument are described as is the relationship between Staple and Fibre based measurements.

By the end of this topic, you should have:

  • an understanding of the limitations associated with subjective appraisal of Staple Length, Staple Strength and Position of Break
  • an understanding of the relationship between Staple and Fibre properties e.g. Staple Length and Fibre Length, Staple Strength and Fibre Tenacity
  • an understanding of the principles of objective measurement on an ATLAS instrument including the requirements of the IWTO Test Method.

Topic 11: Wool Colour Measurement

Colour is one of the most important wool properties because it provides the best indication of the ‘dyeing potential’ of a grower’s lot or an export consignment. Wool of poor colour cannot be used to produce a yarn with a light pastel shade, and extremely poor colour may be associated with microbial damage of the fibres.

On completion of this topic you should be able to:

  • Describe how the human visual system works
  • Explain the terms colour matching functions, illuminant spectral energy function and the spectral reflectance function and describe how they are used to calculate the tristimulus values
  • Explain the terms lightness, hue and saturation and how they describe a three-dimensional colour space
  • Describe the colour space for the CIELAB system in terms of the opponent colours
  • Explain the operating principles of a modern colour spectrophotometer, defining the key parts of the instrument
  • Compare two instrument geometries mostly used for colour measurement
  • Explain the importance of colour measurement for wool and why there is a wide variation in wool colour
  • Explain the specific requirements in wool colour measurement regarding sample preparation, its presentation to the instrument and the calibration procedure
  • Interpret tristimulus results in the new D25/10o colour space
  • Differentiate between the base colour and as-is colour of wool.

Topic 12: Contamination

This topic describes the main forms for “contamination” occurring in the Australian wool clip. Contamination, which is considered a major issue by early and late stage processors, includes man-made fibres, dark and medullated fibres, skin pieces through to chemical residues.

By the end of this topic you should have an understanding of:

  • The source of contamination:
    • contamination of wool origin; viz. urine-stained, pigmented and medullated fibres
    • contamination of non-wool origin, viz. wool packs, farm objects (including baling twine), mill packs and mill objects
  • The problems created by each form of contamination
  • Methods to minimise the risk of contamination
  • Future developments.

Topic 13: Fibre Curvature, Crimp Frequency, Resistance to Compression and Bulk

This topic describes the relationship between the four different measurements of fibre shape, and explores the relationship between these measurements. The four measurements to be covered in this topic are fibre curvature, crimp frequency, resistance to compression and bulk.

By the end of this topic, you should have:

  • an understanding of the measurements of fibre shape
  • an understanding of the principles of measurement of Bulk and Resistance to Compression
  • an understanding of the relationship between Bulk and Resistance to Compression
  • an appreciation of the measurement of Crimp Frequency, and
  • an understanding of the commercial measurement of Fibre Curvature.

Topic 14: Wool Style

This topic describes the visual characteristics used to appraise wool style and examines the relationship between subjective appraisal and objective measurement of wool style. Instruments developed to quantify components of style are described. The importance of components of wool style in processing are quantified and described.

By the end of this topic, you should have:

  • an understanding of the subjective nature of traditional wool style
  • developed an understanding of the components of style and how these may be objectively measured, and
  • an understanding of the impact of style and components of style on early stage processing.

Topic 15: Use of Measurement

This topic discusses the additivity effects of raw wool selection and the decision making process in the setting of raw wool specification and blend engineering along with strategies topmakers employ to optimise price whilst meeting technical top specifications with processing predictions. The topic discusses other forms of prediction models and the pitfalls of only fitting data rather than fully validating data sets.

At the completion of this topic the student will have and understanding of:

  • the commercial importance of objective measurement in topmaking and blend engineering and how prediction formulae are developed and used,
  • an insight into the flexibility of prediction and its benefits.

Topic 16: Fibre Diameter Measurement of Slivers and Tops

This topic covers the methods used to measure the fibre diameter characteristics of slivers and tops. Fibre diameter is arguably their most important property, because of the importance of fibre diameter in the efficient spinning of fine worsted yarns and in the manufacturing light, soft handling fabrics for apparel. The finer the fibres, and the fewer the number of fibres present in a cross section of a yarn produced from the fibres; the more flexible is the yarn. These factors are critical to the quality of wool fabrics.

On completion of this topic you should be able to:

  • outline the method of sampling slivers for fibre diameter measurement
  • explain the operating principles of the Projection Microscope, OFDA100, OFDA4000 and Laserscan for measuring slivers and tops, and compare their advantages/disadvantages
  • use projection microscope results to:
    • construct a suitable table for the data
    • draw a fibre diameter distribution as a histogram
    • calculate the mean fibre diameter, standard deviation and coefficient of variation
  • compare the precision levels possible with the various instruments used for measuring mean fibre diameter.

Topic 17: Future Development in Wool Metrology

This topic briefly describes the framework in which future developments may occur in wool metrology and provides examples of possible developments.

By the end of this topic, you should have:

  • an appreciation of the factors which drive developments in wool metrology; and
  • a guide to possible future developments in wool metrology.

Topic 18: Subject Overview

This topic provides the summaries of all the topics covered in Wool Biology and Metrology.

By the end of this topic, you should have reviewed all these topics.