We have now traced the wool from the sheep’s back as far as the bag, and may assume that the bag has travelled from the shearing shed to the merchant’s or mill’s warehouse. Some foreign wools, notably Australian and South American, are, as we have seen, skirted and roughly graded in the shearing shed, so that, when the bag is opened, there remains only the sorting to do. Grading is the separation of fleeces into classified groups. Skirting is the removal from each fleece of the worst parts, namely, the britch wool, manure locks (known as tags), and matted or kempy portions. Sorting is the dividing of the individual fleece into various classifications.
Wool as Against Hair
Before we take up the grades and sorts in detail, it will be well for us to inquire briefly into the nature of the wool fibre. In the first place, wool differs from hair in that its fibre consists of a core (medulla), a pulp (cortex), and an epidermis. A hair follicle consists of a medulla and an epidermis. Moreover, the epidermis of a hair is closely and evenly scaled, which makes it smooth and lustrous. The surface of a wool fibre is not evenly serrated, which accounts for the felting, or interlocking, quality. Wool in which there is insufficient moisture and natural grease (yolk) frequently becomes felted at the ends. Such wool is variously referred to as cotted, cotty, or brashy. The tensile strength of a wool fibre is low, its elasticity high. The length of the fibre varies from one to over ten inches, and the diameter from .0018 to .004 inches. The better a wool the less like it is to a hair. Generally speaking, the finer the wool, the shorter the fibre, but length alone would not indicate the grade. Pure merino and high cross-bred wools have a close wave, known as crimp, which increases the elasticity and is therefore desirable from a spinning standpoint.
The chemical composition of wool is: carbon 50%, hydrogen 7%, nitrogen 18%, oxygen 22%, and sulphur 3%. It is soluble in alkalies, and at a temperature of 130° C. will reduce to powder.
Shrinkage
Wool before it is scoured contains a large quantity of yolk, or natural grease, and also, besides dust and vegetable matter, a considerable amount of dried perspiration, or suint. The amount of weight lost through the removal of these substances when the wool is scoured is termed shrinkage. It will be readily appreciated that this is a very important factor in connection with the purchase of grease wool. The percentage of shrinkage varies from 20% to 80%. Nevertheless a good buyer will often be able to estimate within one or two per cent. The factors to be considered in this connection are the breed, the soil, the climate, and the care with which the sheep are raised, as well as the diligence with which the fleeces are put up. Fine wools always shrink more heavily than coarse; and pulled wools, since they are washed and brushed during the process, show a very much lower shrinkage than fleece wools. The average shrinkage of United States wools is about 55%. Fine domestics shrink about 60%. Lower grades about 45%. Fine territory wools about 65%; lower grades about 55%. Pulled wool averages about 27%. Fine Australian wools average 49%, for, although they are the finest, the fleeces contain less dirt. Cape wools about 62%, and South American about 51%.
Qualities Desired
The qualities looked for in wool are roughly six, and they vary according to the purpose for which the wool is to be used.
1. It must be fine enough to spin the required number of counts.
2. It must be strong enough to withstand strain of manufacture.