VM is described as the presence of burrs, twigs, and grasses and is affected by feed and grazing conditions. The percentage of VM affects overall price because of high processing costs and fiber loss at the mill. Top is the result of a carding and combing process that delivers a rope of fibers in a parallel configuration in the worsted processing system. Testing for percentage of oil content in top is performed to determine how much oil was added during the carding and combing process. Commercial lots of wool and mohair, alpaca, cashgora, cashmere, dehaired camel, yak, and llama, as well as yarn and cloth samples, are tested for fiber diameter and coarse hair content.
Special testing is performed by request.
Normally, the finer the fiber or the lower the micron count, the higher the commercial value. These standards are reviewed every five years by the ASTM D13.13 committee and either approved or withdrawn. The U.S. Bureau of Customs uses these standards in assessing duty on imported wools and they are used daily in the buying and selling of grease wool and wool top. Average fiber diameter is critical in blending wools from different areas of the United States and from other fiber producing countries of the world to produce the desired end product to meet specifications. Quality control is a continuous process in the measurement of AFD, length, and defects in the textile plant's manufacturing process.