As soon as you begin to handle fleeces, you realise how much they differ. Some are fine and soft to the touch, while others are coarse and feel scratchy to the skin.
The length of individual fibres or hairs that make up an animal's fleece or coat is also an important factor. Longer fibres can be drawn out to make a finer thread than short ones, so this length, called the staple length, therefore helps to decide the use that fibre is suited to.
Woolen fibres have curls, waves or bends along their length. This is called crimp. The more crimp fibres have, the finer they can be spun, or the flatter they can be felted. Fine wool, with fibres of smaller diameter, tend to have more crimp than coarser ones.
When wool became an important commodity there had to be some way of grading or classifying it to determine its use and value. The finest wool, suitable for clothing, has always commanded the highest prices, while coarser wool, suitable only for carpet or rugs, has always been of lower value.
Spinners used to judge a fleece by eye. Taking into account the staple length, diameter and crimp of the fibres, an experienced wool handler could estimate the spinning capacity.
In England, Bradford was at the heart of the wool industry, and it was here that the English system of grading wool was first developed. It was known by several names.The English Worsted Yarn Count System, but more commonly the Bradford System, Bradford Count or Spinning Count. The system quickly spread, and was soon in use worldwide.
The Bradford System required wool handlers to estimate the number of hanks of single ply yarn that could be spun from a pound of the wool "tops". Tops is the name given to wool that has been prepared by cleaning and carding or combing to leave all fibres running parallel to one another.
A pound of 64' s would make 64 such hanks - a total length of over. 20 miles. The finest wool with the best crimp would make the most hanks - upto about 60, and command the highest price. The coarsest but strongest wool might be only 30's. In this way wool count be classified into groups such as 44's to 46's, with all wool within a group being the same price.
The disadvantage of the Bradford System was that it relied on the expertise, good judgement and honesty - or otherwise - of the seller or market graders. The world needed a grading system that used provable measurements rather than estimations.
In the United States, official standards were introduced which used ranges of average fibre diameter (AFD) and standard deviation (SD) from that average. These ranges were then assigned to Bradford Counts. So for example wool with an AFD of 28.60 - 30.08 microns was called 54's. A micron, incidentally, is a millionth of a metre. It is measurable by anyone with a micrometer that goes down to 1 mm and a high power microscope. Confusing though this system could be, with the AFD running downwards with increasing quality, and the Bradford Count System it linked to running up, for the first time the value of this expensive commodity could be easily proven.
A guide to wool grades according to diameter in microns is:
Fine - 17.7 or less - 22.04
Medium 22.05 - 30.99
Coarse - 31 - 36.19
Very Coarse - 36.2 - 40.2 or above.
The variation in thickness or diameter of fibres within a batch of wool is an important factor. The degree of variation from the average diameter is known as the Standard Deviation or the Coefficient of Variation. It is calculated as a percentage and assigned a grade thus...
Less than 21 % Excellent
22% - 27% Average
Over 27% Poor
A batch of wool with poor SD will be dropped down a grade. Micron testing wool with a poor SD will be of little value as you could be testing the finest when the quality is actually going to be pulled down by the coarsest.
A third system was developed in America in the early 1800's known as the Blood System. This was at the time when merino sheep with fine fleece were being imported from Spain to improve the coarse wool native sheep. The system assumed that cross breeding would produce lambs with fleece of intermediate quality. Therefore wool was graded according to the percentage of merino blood in the sheep. Grades were Fine, 1/2 blood, 3/8 blood, 1/4 blood, low 1/4 blood, Common and Braid. Fine equated to upto 64's in Bradford terms , Low 1/4 would be coarse around 44's, and Braid was very coarse. 40's or less. The Blood System is rarely used today, perhaps because we know that crossing doesn't always give an exact percentage of intermediate wool, but the three systems are directly compatible.
Over the last ten years other measurements of fibre size and character have developed around the world, but Bradford's Spinning Count will remain in use for a long time.
Other factors such as general condition and cleanliness also effect grading and value of wool. A point worth noting is that a batch of wool will be down graded by dirty, coarse or weak fibres within it. This can be an important factor for people selling through a wool pool or sending mixed qualities to a market or the British Wool Board.