Snowmass Alpacas

Genetics by Design
Methods for Measuring Micron
(By Angus McColl, Yocom-McColl Testing Laboratories, Inc.)

Objective fiber testing can be a powerful marketing and genetic selection tool when used properly. Objective measurement is an assessment made without the influence of personal feelings or prejudice. Visual appraisal and fiber handling are fundamental aspects of fiber judging, but are very weak appraisal methods for accurately identifying average fiber diameter. Instrumentation can accomplish the measurement of fibers with accuracy in the tenths of a micron (one millionth of a meter). The difference between a sample averaging 20.5 microns and one at 22.5 microns is very small in physical terms, but it is critical in terms of commercial use and pricing structure.

Fiber testing technology gives breeders a useful tool to analyze fiber and track the progress of their selection programs. The determination of average fiber diameter helps identify the best end use for fiber and is information that mills require before making their purchasing decisions.
The ability to provide accurate information on fiber quality places natural animal fiber producers in a stronger position to sell their fiber for what it is worth. Very few people buy and sell commodities without knowing everything they can about them. Information is power in the marketing world, and objective fiber assessment provides it.

Instruments in the Lab
There are four approved instruments and methods, the most widely used instruments now being OFDA 100, and Sirolan LaserScan. Their development followed many years of use of the Airflow and Projection Microscope, which are both still in use. Test methods are approved by the International Wool Testing Organisation (IWTO) and the American Society for Testing and Materials (ASTM) and are performed in laboratories under standard conditions for testing textiles, i.e., 70° F, and 65% relative humidity (+2% RH). Yocom-McColl in Denver, CO has all four instruments, but performs fiber diameter testing using only LaserScan, OFDA 100, and microprojection.

Sirolan LaserScan, (CSIRO), and Optical Fibre Diameter Analyser, (BSC Electronics) were both developed in Australia. These two instruments are calibrated using Interwoollabs tops, the only recognized supplier of calibration tops to the worldwide textile industry.
laser scanner alpaca fiber
A diagnostic and calibration check is performed each day on both instruments. For samples averaging 26.0 microns and finer, the accuracy of measurement is plus or minus 0.2 microns when the tests are performed properly under standard conditions.

The LaserScan instrument measures fibers by dispersing individual snippets (two millimeter lengths of fiber) in a solution of isopropanol and water and this fluid transports the fibers through a glass cell where each one intersects a laser beam. The LaserScan measures the change in the signal generated when the shadow cast by the fiber snippets falls on a light detector. The signals, which are directly proportional to the fiber diameter, are recorded electronically and analyzed almost instantaneously by computer.

Optical Fibre Diameter Analyzer
Optical Fibre Diameter Analyser (OFDA)
OFDA 100 was approved as an IWTO standard in 1995. Mark Brims and his company, BSC Electronics, designed the instrument. It uses a video camera to produce electronic images of magnified fibers which are distributed over a horizontal glass slide. Software analyzes the fiber images and derives measurement of diameter of a large number of longitudinal fiber sections. OFDA 100 also measures and calculates the distribution of fibers (SD and CV) as well as average fiber diameter and several other fiber diameter related characteristics. Both of these methods provide the wool and textile industry with high volume testing applications.

Airflow Analyzer
Airflow measures the flow of air through a sample of wool and provides an indirect measurement of average fiber diameter. It does not give measurements of standard deviation and coefficient of variation and must be calibrated using wool samples that were originally measured by microprojection. Airflow assumes wool density is always constant, and this has caused problems with wools that are less dense (particularly those containing medullated fibers). According to the Australian Wool Testing Authority (AWTA), Airflow can also be affected by large variations in Coefficient of Variation (CV), providing coarser results with a large CV and a finer result with a lower CV. It was the normal measurement for micron results in Australian wool auctions until the summer of 2000.

Portable Instruments (OFDA2000 and Fleecescan)
OFDA2000 and Fleecescan are two instruments developed in Australia for on-farm fleece testing with the objectives of separating superfine wool from flocks of fine-wool sheep and assisting with genetic selection based on fineness characteristics. The reason for the former practice is a premium paid for superfine wool. One of the problems of measuring purely for marketing reasons was in many cases when the superfine wool was removed from the clip, the remaining wool had a higher micron with a lower market value. The additional labor and testing expense to separate the superfine wool is not always economically justifiable.

The OFDA2000 and Fleecescan are not approved by IWTO or ASTM. Wools separated into different micron ranges by these instruments still have to be core sampled and tested by IWTO and/or ASTM approved methods and instruments when offered for sale.
The OFDA2000 measures the dimensions of raw (i.e., greasy and dirty) fibers and then uses a constant correction factor (within a "mob") to estimate the true dimensions. This correction factor is measured and calculated on-site and is typically the average of 30 samples. Since the cleanliness of every sample measured is different, this practice limits the accuracy of individual measurements.

The OFDA2000 has a built-in compensator for temperature and relative humidity that adjusts for the ambient air at the testing location. Thus it can only be properly used on samples that have been given time to reach equilibrium with the ambient air. OFDA2000 is not suitable for testing raw, unconditioned samples at a central location since raw samples from different areas of the country contain varying amounts of moisture that affect fiber diameter. Also, it would not be possible to use an appropriate grease correction factor. The only way to accurately test wool or other animal fibers is for the samples to be washed, dried, and conditioned at standard conditions for testing textiles, a worldwide requirement.

The OFDA2000 tests fewer than 100 fibers (depending on the fiber diameter and staple length) from tip to base in five millimeter increments for a total of about 1500 measurements.
It produces a fiber profile reflecting aging, health/production status, and environmental conditions the animal was subjected to during the growth of that particular staple length. Typically, a mid-side sample is measured to estimate the average fiber diameter of the whole fleece. Other (more accessible) locations (e.g., the pin bone) have also been investigated.
The OFDA2000 uses the same basic technology as its parent the OFDA 100 with the exception of measuring multiple fibers in profile. The OFDA 100 is actually capable of measuring one fiber at a time in profile but this measurement is slow and tedious, and probably only used by researchers.

The Fleecescan is transported in a trailer. This system minicores each fleece and chemically cleanses the sample that is then tested on a specially designed LaserScan heavily protected to avoid damage as it is being moved.

Genetic Selection Tool
Yocom-McColl uses both LaserScan and OFDA 100 to test fiber of individual animals. We can measure average fiber diameter, diameter distribution, spin fineness, curvature, curvature distribution, and comfort factor on the LaserScan. Using the OFDA 100, we measure all of the above plus medullation on white or light-colored animals. Comfort factor is the percentage of fibers greater than 30 microns subtracted from 100 percent (in other words, a marketer’s positive "spin" on the original term "prickle factor".

We test individual animals using two millimeter snippets obtained across the base of the two inch square submitted sample. In this way, we are able to provide estimates of the genetic uniformity of the sample at a precise environmental time.

The Laserscan and the OFDA 100 test from 2,000 to 4,000 individual snippets per sample either core sampled (minicored) or guillotined. When guillotined at the base of the staple, all fibers measured were produced at the same time and in the same environment. Such a measurement indicates the genetic fineness and uniformity of the animal (at a specific age) that can be extremely valuable for selection purposes.

Neither LaserScan nor OFDA measure relaxed staple length. Yocom-McColl measures average staple length on an Agritest instrument according to IWTO 30 on relaxed, conditioned staples.

Fiber Testing Terminology

Normal Distribution
The graph of a normal distribution, the normal curve, is a bell-shaped curve. Many biological phenomena including animal fiber diameter distributions for single-coated animals, result in data distributed in a close approximation to normal. Hence, statistics applicable to normally distributed populations (mean, standard deviation, and coefficient of variation) are used to define these fiber diameter distributions. The normal curve is symmetric about a vertical center line. This center line passes through the value (the high point of the bell) that is the mean, median and the mode of the distribution. A normal distribution is completely determined when its mean and standard deviation are known.

Approximately sixty-eight percent of all measurements lie within one standard deviation of the mean and approximately 95.0 percent of all measurements lie within two standard deviations of the mean. More than 99.5 percent of all measurements will lie within three standard deviations of the mean.

Fiber Diameter Measurement and Distribution
Fiber diameter is measured in microns. One micron is equal to 1/1,000,000th of a meter or 1/25,400th of one inch. Mean Fiber Diameter (MFD) is in common use internationally. MFD, Standard Deviation (SD) and Coefficient of Variation (CV) all relate to the (approximate) normal distribution of the animal fiber diameters. SD characterizes dispersion of individual measurements around the mean.

In a normal population, 66% of the individual values lie within one SD of the mean, 95% within two SD’s and 99% within 2.6 SD’s. Since SD tends to increase with increasing MFD, some people prefer to use CV (=SD*100/MFD) as a method of comparing variability about different sized means.

Comfort Factor
Comfort factor is the percentage of fibers over 30 microns subtracted from 100 percent. Ten percent of fibers over 30 microns corresponds to a comfort factor of 90 percent.

Fiber curvature is related to crimp. Average Fiber Curvature (AFC) is determined by the measurement of two millimeter (2mm) snippets in degrees per millimeter (deg/mm). The greater the number of degrees per millimeter, the finer the crimp. For wool, low curvature is described as less than 50 deg/mm, medium curvature as the range of 60-90 deg/mm, and high curvature as greater than100 deg/mm.

Typical values might be illustrated by a 30 micron Crossbred wool fleece with typically low curvature and broader crimp with a frequency of approximately two crimps/cm. In contrast, a 21 micron Merino fleece typically has a medium curvature and a medium crimp with a frequency of approximately four (4) crimps/cm. A 16 micron Superfine Merino fleece typically has a high curvature and a fine crimp with a frequency of approximately seven (7) crimps/cm.

Definition of Medullation
A medullated fiber is an animal fiber that in its original state includes a medulla. A medulla in mammalian hair fibers is the more or less continuous cellular marrow inside the cortical layer in most medium and coarse alpaca fibers. By definition (ASTM), a kemp fiber is a medullated fiber in which the diameter of the medulla is 60% or more of the diameter of the fiber.

Medullation Measurement
Medullation measurement can be performed using either a projection microscope or the OFDA 100. Using IWTO nomenclature, a kemp fiber is classified as an “objectionable fiber” when measured on the OFDA 100. The OFDA100 measures opacity and therefore only white or light colored fibers can be measured. A reasonable assumption is that colored fibers have similar levels of medullated fibers as their white and pastel counterparts.

Spinning Fineness
This number (expressed in microns) provides an estimate of the performance of the sample when it is spun into yarn by combining the measured mean fiber diameter (MFD) and the measured coefficient of variation (CV). The original theory comes from Martindale, but the formula used comes from Butler and Dolling and normalizes the equation so that the spinning fineness is the same as the MFD when the CV is 24%.

Length & Strength
Length is measured in millimeters (mm) and the reported measurements readjusted to an annual growth period. Strength is measured in Newtons/kilotex (N/ktex) and is the force (measured in Newtons) required to break a staple of a given thickness (measured in kilotex). On the earth’s surface, one kilogram exerts a force of 9.8 Newtons (= 1kg * acceleration due to gravity measured in meters/second2). Kilotex indicates thickness in terms of mass per unit length expressed as kg/km.

Intrinsically, alpaca fibers appear to be very strong, an average of 50 N/ktex or better is not unusual. From a processing point of view, a mean staple strength greater than 30 N/ktex is considered adequate for pro-cessing wool on today’s high-speed equipment.
Resistance to Compression
The resistance to compression (RTC) of alpaca fibers is measured in kilopascals (Kpa). A pascal (Pa) is a unit of pressure equivalent to the force of one Newton per square meter. In the commercial sector, RTC values >11 kPa are considered high, 8 to 11 kPa medium, and <8 kPa is low. The intrinsic resistance to compression of alpaca is low because of the relatively low levels of crimp. Thus, alpaca is not suited to end-uses that require high resistance to compression (or high bulk).

Position of Break
Truly sound fibers break in the middle section of the staple. Intrinsically, alpaca fibers appear to be very strong, in the 50 N/ktex range. A mean staple strength greater than 30 N/ktex is considered adequate for processing wool on today’s high-speed equipment.

Clean Yield
Yield is based on bone-dry, extractives-free wool (alpaca) fiber or wool (alpaca) base (WB). Many different “commercial” yields are used in the international marketing of wool fibers. These are values calculated to predict the amount of clean fiber obtained after commercial scouring and/or after combing. Allowances are typically made for grease, ash, vegetable matter, and moisture. Various percentages of moisture are added in these calculations of commercial yield, which in some cases (very clean wool or some alpaca yields) may result in the clean yield exceeding 100%.