Weigh the materials to be scoured before soaking in hot water. You can wash any fabric in the washing machine prior to scouring if you want.
Recipe is for 100 grams of material to be scoured, so you might have to do some math if the weight of yours is different.
Large stock pot of enamel or stainless steel. Fill pot 2/3 full of water
Add 35 grams of soda ash for every 100 grams (dry weight) of materials to be scoured. Add materials to the pot and bring to a boil. Be careful to not let it boil over. Adjust to high simmer and simmer for a minimum of 2 hours, stirring every 15 minutes (longer for linen). Allow to cool enough to handle the materials without burning yourself. If water is extra dirty, repeat.
Rinse and use immediately for mordanting or dyeing, or let dry.