Classification of U.S. Cotton
High Volume Instrument (HVI) classing has been available on an optional basis to all growers since 1981. In 1990, the National Advisory Committee on Cotton Marketing, an industry-wide committee representing growers, exporters, manufacturers, ginners and warehousemen, recommended that HVI measurements be required for any Upland cotton which might be placed in the government’s price support program, effective with the 1991 crop. As a result, virtually all of the U.S. Upland cotton crop is now HVI classed.
For each bale classed in 2007, the following quality information was provided:
|Measure of the average length of the longer one-half of the fibers (upper half mean length), reported in both hundredths and thirty-seconds of an inch.|
|Determined by dividing the mean length of the fibers by the upper mean length and reported as a percentage. The higher the percentage, the greater the uniformity. If all the fibers in the sample were of the same length, the mean length and the upper half mean length would be the same, and the uniformity index would be 100. However, cotton fibers within a sample vary considerably, so length uniformity would be less than 100.|
|A measure of fiber fineness represented by the air permeability of a mass of cotton fibers compressed to a fixed volume. Measurement is performed on an instrument known as a micronaire, and the measurement is commonly referred to as “micronaire” or “mic.” The information is used to determine the relative size or fineness of fibers. The micronaire reading can also provide a relative indication of fiber maturity, or cell wall thickness, for varieties of cotton with similar fiber perimeters.|
|Strength is reported in grams per tex. A tex unit is equal to the weight in grams of 1,000 meters of fiber. Therefore, the strength reported is the force in grams required to break a bundle of fibers one tex unit in size.|
|The color of cotton is measured by the degree of reflectance (Rd) and yellowness (+b). Reflectance indicates how bright or dull a sample is, and yellowness indicates the degree of color pigment. A three-digit color code is used to indicate the color grade. This color grade is determined by locating the quadrant of the color chart in which the Rd and +b values intersect. For example, a sample with an Rd value of 72 and a +b value of 9.0 would have a color code of 41-3.|
|Trash in raw cotton is measured by a video scanner, commonly referred to as a trashmeter. It is a measure of both leaf and other elements such as grass and bark. The surface of the cotton sample is scanned by the camera, and the percentage of the surface area occupied by trash particles is calculated.|
There are 25 color grades and five categories of below grade color. The White, Light Spotted, Spotted, Tinged and Yellow Stained grades are listed in a viewable table.
There are seven leaf grades, as well as one below leaf grade category. The leaf grades are listed in a viewable table. Explanatory terms considered necessary to describe abnormal conditions are entered on the classification memorandum or certificate. The quality of the cotton is normal unless otherwise noted.
HVI Classification of Pima Cotton
Fiber properties are also measured for American Pima cotton. While the basic testing procedures for American Pima cotton are the same as for American Upland cotton, different grade standards are used because of the genetic differences in Upland and Pima and the different ginning methods used. As American Pima cotton is ginned on roller gins, rather than saw gins, its appearance is not as smooth as that of Upland. Also, the color of American Pima is more creamy than that of Upland.