Only certain types of fibre can be wet felted successfully. Most types of fleece, such as those taken from the alpaca or the Merino sheep, can be put through the wet felting process. One may also use mohair (goat), angora (rabbit), or even certain dog hair. These types of fibre are covered in tiny scales, similar to the scales found on a strand of human hair. Wetting and soaping the fiber causes the scales to open, while agitating them causes them to latch onto each other, creating felt. Plant fibres and synthetic fibres will not wet felt.
A subset of wet felting is nuno felting. It is a technique developed by Polly Stirling - a fibre artist from Australia. The technique bonds loose fibres, usually wool, into a sheer fabric such as silk gauze, creating a lightweight felt.
Needle Felting
Needle felting is a popular fibre arts craft that creates felt without the use of water. Special needles that are used in industrial felting machines are used by the artist as a sculpting tool. While erroneously referred to as "barbed" needles, they in fact have notches along the shaft of the needle that grab the top layer of fibres and tangle them with the inner layers of fibres as the needle enters the wool. Since these notches face down towards the tip of the needle, they do not pull the fibres out as the needle exits the wool, unless a reverse needle is used (with this desired effect).
Once tangled and compressed using the needle, the felt can be strong and used for creating jewellery or sculpture. Finer details can be achieved with this method using a hand-held tool with either a single needle or a small group of needles (2-7), so it is a popular technique for producing 2D and 3D felted work.
Certain artificial as well as natural fibers can be needle felted. Most of the machine needle felt is synthetic.
Carroting
From the mid-17th to the mid-20th centuries, a process called "carroting" was used in the manufacture of good quality felt for making men's hats. Beaver, rabbit or hare skins were treated with a dilute solution of the mercury compound mercuric nitrate. The skins were dried in an oven where the thin fur at the sides turned orange, the colour of carrots.
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Pelts were stretched over a bar in a cutting machine, and the skin was sliced off in thin shreds, with the fleece coming away entirely. The fur was blown onto a cone-shaped colander and then treated with hot water to consolidate it. The cone then peeled off and passed through wet rollers to cause the fur to felt. These 'hoods' were then dyed and blocked to make hats. The toxic solutions in the dye and the vapours it produced resulted in widespread cases of mercury poisoning among hatters, which may have been the origin behind the phrase "mad as a hatter".
