ashing or Scouring

The goal of scouring is to separate and remove contaminants from the fiber. The primary contaminants in animal fiber are lanolin (in sheep wools) and body oils, suint (dried sweat), dirt, dung, and veg. It is also possible that the animals could pick up chemicals from pesticides and herbicides used in or near their pastures.

All of these except lanolin, body oils, and veg are generally water soluble (it's certainly possible that some of the chemicals used in herbicides and pesticides aren't - I don't know). So, it's possible to clean most fleeces simply by repeated soaking in cold water -- a long term project if ever there were one. Cold soaks though, won't get lanolin out of a sheep fleece nor will soaking be as likely to get the fleeces as clean as they might be were they scoured with hot water and soap or detergent.

There are basically two ways to get lanolins and oils into a form that is water soluble: emulsify or saponify. Saponification converts lanolin and oils into soap which can then be rinsed away with water. Making the wash water alkaline will saponify the oils and lanolin. Washing soda mixed with the wash water will do this. But, care is required because the alkaline conditions will damage the fiber.

The other process is create an emulsion. An emulsion is a mix of two normally unmixable liquids - oil and water are the classic example. Emulsions occur when small particles of one liquid are suspended in another. The agent required to emulsify the lanolin and oils in water is a surfactant. The most ubiquitous surfactants are detergents. The polar molecules of the surfactant bond with droplets of lanolin and oils and also bond with the water. Hot water aids in the emulsification process by liquefying the lanolin and oils.

Because soaps and washing soda are alkaline (high pH) I use neutral pH detergent to wash fleeces. Hot water (140ºF/60ºC) and a generous amount of detergent have proved sufficient to clean even the most awful, nasty smelling, stickiest, buck angora (mohair).