Scouring in regard to fibers means: to free or clear fabrics or fibers from impurities like dirt, grease, pectins. The word 'scouring' is most used in relation to wool, cotton is 'boiled out', silk is 'boiled off' or de-gummed.
Scouring is an essential pre-treatment for mordanting, printing and dyeing. This is mainly because the fatty and waxy impurities form a barrier for the even uptake of mordants and dye stuffs resulting in lighter, uneven or blotchy results.
PFD means Prepared For Dyeing. RFD means Ready For Dyeing. Materials that are sold as PFD may not need any additional scouring.
Previously loved fabrics that have been washed well multiple times usually do not require extra scouring.
Raw wool fleece contains easily up to 60% of grease (lanolin), sweat residue (suint), pectins (grass residue), poop and other dirt.
These must all be removed before spinning and weaving. Processed wool fabrics usually come PDF and do not require any heavy scouring. As a rule of thumb: if the fabric of yarn has a heavy sheep smell you should scour it.
Silk, especially so-called raw or wild silks have 20-30% of sericin, some albumen and a thin layer of gelatin. Scouring these impurities is called de-gumming.
Domestic mulberry silk like habotai, satin, and crepe de Chine is already de-gummed, that is why it is shiny.
Removing the sericin can damage the fibroid, which is the actual silk fiber. You can easily overdo it and damage the lustre and hand of the silk.
Because sericin is a protein it will uptake dyes very well, and I do not recommend removing it at all when you are working with wild silks.
If you are working with handwoven silks there most probably is a lot of starch in the finished product that is easily removed (see below).
Cotton can contain small pieces of wood and cotton husks. Most likely it will contain pectins, wax and weaving grease, which are oils that are used in the weaving process to prevent snapping of warp and weft yarns and smoothen the weaving process.
Handwoven cotton often has starches like rice milk applied in the final process of ironing. Commercial cotton can contain optical brightness, teflon-like coatings and starches to manipulate the 'hand' of the fabric.
Linen/flax. Linen and other bast fibers can contain pectins, lignin, and relatively little wax and fat. Flax fibers are highly crystalline, which gives them high tenacity but also makes them less stretchy than cotton.
Scouring silks and wools.
For scouring you can use; Either; A spoon of delicate wash ph neutral detergent. or Castille soap; 1 spoon per 4 litres of water or Orvus Paste: the amount of Orvus paste should be 1% of the weight of fibre. Dissolve in hot water before adding to the pan. For a proper scour, put the fibres in a clean pot with plenty of water for the fabric to move around. Slowly slowly bring the fabric to a simmer of 90 degrees but NOT boiling, for at least 30 minutes. Let the fabric cool down in the pot, so as not to create a thermic shock. Strain of the water and rinse once more with cool water. You can now dry and store the fabric until further use, marking it ‘scoured’.
Scouring cellulose.
For scouring cellulose you will need soda ash and dish washing detergent. Dish washing detergent is a very economical and readily available resource for cleaning fabricsand it functions as a wetting agent.
Usually a good ratio is 1:10 so if you have 500 grams of fabrics you need 50 grams of soda ash and 50 grams of dish washing detergent.
Dissolve the cleaning agents in plenty of water. Add fabrics. and top up with water to cover. Bring this all to a boil. and stir regularly for about an hour. Let cool for 30 minutes and rinse the fabric. If the water is *very* brown you may have to do another cycle.
Scouring in the washing machine.
You can use a washing machine on long boiling cycle if you have a lot of fabric, that works really well. Our washing machine can take 8 kilos fabric on a boiling cycle that takes 3.20 hours. You just add the soda ash to the washing powder tray. I use 5 spoons of soda ash for a load. Do not add dishwashing detergent because the foam will get crazy off the charts!
Scouring with enzymes
Enzymes can break down a lot of pectin and waxes. I use diastatic malt enzyme which is available on Ebay and Amazon. It is used in bread- and beer making.
Put half a cup of diastatic malt enzyme dissolved in a bucket tepid water, mix well, add fabrics and work well in the solution. Let this sit overnight and then continue with a good wash in the washing machine.
Removing starch from delicate fabrics.
If you have handwoven, or other delicate fabrics that have a coating of starch, you do not need to do a full scour but you do have to remove the starch and dust. A great example is eri silk scarves, that do not need any scouring but do need to have their starch removed.
How -t0: Add half a cup of heat bran to a bucket of water. Add fabric. Mix well. Let this sit overnight and rinse the following day.