At its most basic, scouring is a way of cleaning textile fibres. Wool that’s been shorn from a sheep is known as greasy, or raw wool. Just under 50% of raw wool isn’t actually wool at all: it’s grease, dirt, sweat (suint), burrs and seeds. Many other animal fibres also get washed: alpaca, goat hair and silk all get some level of cleaning. Angora rabbit is apparently an exception. Plant fibres have different processes, although decortated hemp does have a degumming stage.
So many ways to clean fibre!
Raw fibre often contains burrs that can scratch, and may contain disease that can transfer to humans, so it should be treated with caution. Cleaning removes the danger of disease and some burrs. There are many different traditions and ways to wash and scour a fibre. In this context, washing aims to remove large particles and sweat. Scouring uses heat to remove the oils from the fibre. Some people choose not to scour their fibre, because the oils can help the spinning process. Greasy wool is also more water resistant. Wool grease can develop a distinctive smell and gum up modern spinning equipment that is made for clean wool.
Some farmers wash their own fibre, using detergent. Ruth McGregor gives a good description of the process. Their products have what some people believe is a more natural ‘feel’. It’s particularly easy to do this with fibres like alpaca, which don’t have much grease. They do remain rather dusty though! Different sheep breeds have different levels of grease. For example, a Gotland sheep fibre will feel cleaner without scouring than a Merino sheep fibre.
Another way to clean wool fibres is to ferment them. This process uses the oils and sweat already present in the wool to ferment a soap. Zoe had me giggling and in awe over her experiment with this process.
How big business does it
Most commercial fibre you buy is scoured. There are two commercial scouring methods: an aqueous (water) process, and an organic solvent process. Scouring in Australia commonly uses the aqueous process. This process uses large amounts of water, heat and some detergent. The raw fibre gets dropped into 4 – 8 bowls (wash tanks) of hot/warm water and moved around to clean it. After each dunking, excess water is squeezed from the fibre before it drops into the next bowl. Each bowl contains cleaner water than the one that preceded it.
- 150kg of wool grease
- 40kg of suint
- 150kg of dirt (in Australia it averages around 180kg)
- 20 kg of vegetable matter (although this is likely higher in Australia because we have lots of burrs in our grass)
- 640kg of wool fibre.
Any grease in the washing water is spun off and sold to be made into lanolin. Solids can be separated from the wash and sent to landfill or composted for agricultural use. The washing water can be recycled up to a point, but scouring plants can still go through up to half a million litres of water a day. Scouring plants in Australia must treat water on their site until it’s safe to add to the sewerage system, or apply to the land. In Melbourne, all the scouring plants are city-based. This means they treat their water on site, then our excellent sewerage system takes over.
After scouring, fibre might be carbonised with sulphuric acid or bleached with hydrogen peroxide. Carbonising removes high levels of vegetable matter and softens the fibre. Bleaching brightens the colour of the wool. Not every plant undertakes these steps; I saw how they are done at Victorian Wool Processors.
The final step is to dry the fibre, using drum rollers.
Scouring has a big environmental impact. It uses large amounts of water (whether it is performed at home or commercially). Depending on the type of wool and equipment used, typically 8-20 litres of effluent liquids are created per 1kg of greasy wool. In some ways a commercial system is preferable, because it can recycle its water several times before disposal.
Waste water is high in potassium and nutrients, particularly nitrogen (although not always in a form accessible to plants). A consideration for Melbourne is that scouring works best with soft water. Our drinking water is soft, but our bore water (which local scouring plants may access as well) is hard. It’s possible to soften water, but those additives pose disposal challenges.
Electricity use is high if heat or extraction processes are applied. There are also many biological and chemical contaminants to deal with. The biological contaminants (like grease and weed seeds) often arrive with fibre from the farm. They need to be dealt with at the scouring disposal stage. The chemical contaminants also arrive direct from the farm (like inorganic fertilisers or biodegradable pesticides), or are added during cleaning (like detergents and bleaches). Sodium sulphate, a byproduct of carbonising, needs proper treatment before application to the land.
The (old) Australian scouring effluent standards say that these contaminants can have a big environmental impact, but this can be mitigated with good management. The Global Organic Textile Standard prohibits use of endocrine disrupters (which can be found in detergents) and phosphates. It restricts bleaches to oxygen bleaches only. There’s a lot more detail in these standards that I can’t comprehend. I’d love to have someone’s more educated view on these documents and what they mean for this process.
What does this mean for consumers?
Washing and scouring fibres is a part of clothing manufacture. Few of our animal fibre clothes will skip this process. While fibres like alpaca and goat don’t need intensive scouring, in Australia they’re often processed like wool so the difference in impact is negligible. Even processing fibre at home will still use a significant amount of water, which needs to be disposed of appropriately.
A proactive approach could be to remember that scouring is a process we shouldn’t approach lightly. Let’s use it when we need something new, but try to reduce how often that happens.
Where does scouring happen in Melbourne?
EP Robinson, Geelong
edited on 11/1/16 to add details about disease risk in raw wool