Classification of U.S. Cotton
Cotton classification is the process of describing the quality of cotton according to the official cotton standards. High Volume Instrument (HVI) classing became available on an optional basis to all growers in 1981. In 1990, the National Advisory Committee on Cotton Marketing, an industry-wide committee that represents U.S. growers, exporters, manufacturers, ginners and warehousemen, recommended that HVI measurements be required for any Upland cotton that 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.
Leaf refers to small particles of the cotton plant’s leaf that remain in the lint after the ginning process. Upland leaf grades are determined by the HVI and are identified as numbers 1 through 7.
Measure of the average length of the longer one-half of the fibers (upper half mean length), reported in 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.
Fineness and maturity in combination are measured by resistance to airflow. Air is forced through a specimen of specific weight compressed to a fixed volume. The resistance to airflow is related to specific surface area of the fibers and is a function of both the fiber fineness and maturity. The measurement is commonly referred to as “micronaire” or “mic.” This has an effect on how well the fiber accepts dye and the overall appearance of the fabric. Variation in color within one piece of fabric could indicate poor blending or extreme micronaire limits.
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.
There are 25 color grades and five categories of below grade color, which are divided into five key color grades and further divided into various sub grades. The five main color grades are: White, Light Spotted, Spotted, Tinged and Yellow Stained. In addition, there are seven leaf grades, as well as one below grade leaf grade category.
Trash or foreign matter in raw cotton is measured by a video scanner, commonly referred to as a trashmeter. It is a measure of both leaf and other non lint materials 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.
HVI Classification of Pima Cotton
Fiber properties/qualities 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 cotton, as well as the different ginning methods used. Since 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 creamier than that of American Upland cotton.