Scouring fibres or fabrics is the term used for removing dirt or grease through scrubbing or washing them with a detergent, depending on the kind of fibre used. Scouring is needed if you want to dye the fibre afterwards, otherwise the dye will stick to the dirt instead of to the fibre and will be gradually rub off in the future.
If you buy wool slivers or yarn and you are sure that they have been cleaned thoroughly, there is no need to go through the scouring process.
If you use wool fleece, soak the wool in water overnight. The next morning remove the water (you can use it for watering your vegetables). Repeat this until most of the dirt comes out of the wool. Adding a bit of warm water makes it easier, however be very carefull not to create any sudden shock for the wool by putting it from cold straight into hot water. Most wool has felting qualities and it can start felting during the washing process if handled in a rough way or by sudden temperature changes. Next time, add wool washing liquid to the water and let the wool soak for a while. More dirt will come out, together with the grease. You might need to repeat this several times, until the water is totally clean. Rinse and dry the wool or keep it wet if you are ready to start the dyeing process.
Silk fibres, yarn or fabrics need to be degummed. Often it has been done before you purchase the silk, I tend to do the scouring anyway, just to make sure that no residues are left. Gradually heat up the silk in a solution of water and soft soap. Bring it close to boiling and keep it at that temperature for approx. an hour. Boiling takes away some of the beautiful lustre of the silk, so it is better to avoid it. Let it cool down. If the silk is still sticky, repeat the process. Otherwise rinse the fibres or fabric and dry.
Your material is now ready for mordanting, which I will explain in another post.