Color Grown Organic Cotton, fresh off the bolt

Dyeing with natural dyes is fun fun fun. Before you get there however there are a few crucial steps. Step one: The deep clean - AKA Scouring. If you want good colors on cotton there is no getting around the boil and trouble side of things. There is a big difference between how you clean silk or wool and how you need to clean cotton. In this post I will focus on cotton. If you treat silk or wool like this you will be the very sad owner of a pot full of felted sticky yuckiness. Linen and hemp also have their own gentler process. The following is the Soda Ash process for cotton, remember right practice right fiber.

Scouring really isn't such a lot of fuss - though it does require a pretty big pot if you want to do yardage. I am lucky to have two 10 gallon pots to do my bidding. I try to only put 1,000 grams of stuff in it, but sometimes push it to near 1,400. It is pretty terrifying what comes out of seemingly clean cloth. There are a lot of seed oils, waxes and general guck in cotton that needs to be removed before successful dyeing can commence. A funny thing about cotton is that scouring it requires heat, and often mordanting and dyeing can be done cold. Go figure.

Determining out how much you can fit into your pot with enough room for stuff to move about without being crowded is key. One of the many facts to keep in your Dye Lab Journal is the capacity of your pots. Also it is best if you have separate dedicated equipment for dyeing. Not a good idea to use pots etc for food after use in the dye lab. A non-reactive pot is called for. This means stainless steel or un-chipped enamel. Old canning kettles, and crab pots are good. Mine were purchased at a used restaurant supply store. Because I had a business doing production dyeing I am pretty well set up. All of this can be done more modestly of course. Keep an eye out at thrift stores and garage sales.

Most books that talk about scouring have you figure out the amount of soda ash you need based on the weight of Goods, or WOG. This has never made much sense to me, knowing that what is important is getting the pH high enough to dissolve the waxes etc out of the cotton. So I weigh out the soda ash in relationship to the volume of the water.

Conceivably you could wash your fabric in the washing machine using really hot water and plenty of detergent several times - this is why used cloth is essentially pre-scoured.

It can be amazing what comes out of seemingly clean cotton.

Supplies needed:

A pot big enough for what you need to scour. Experience will tell you how much you can fit in the pot you are going to use. The cloth needs room to move without being unduly crowded. My 6 gallon pot fits a around 650 grams of material. The 10 gallon pots can just barely handle 1,400g if I am diligent about stirring.
A few buckets
Scales to weigh stuff. Small kitchen scales are nice. Using metric will make your math 100,000 times easier. If you fear the metric system because of propaganda use this as a opportunity to free yourself. Over the years I have found various old spring scales and my mother's special friend fixed up an old very precise lab scale for me which I use for most things. A battery powered kitchen scale can be found for $20.
Rubber gloves- I purchase mine at the hardware store, the black ones that are chemical resistant. These last like five thousand times longer than the dishwashing gloves from the grocery store.
Clean water
Stir sticks or a big spoon
Heat resistant glass measure cup - I use a big 8 cup pyrex one.
Sodium carbonate AKA Soda Ash or washing soda. Washing Soda can be had at the grocery store.
Synthrapol or other detergent (Synthrapol is made especially for washing textiles, it is fancy and nice but you can substitute other detergent, including dishwashing detergent if you need to.)

So here is the Scouring process:

Weigh your goods. Note the weight - write it down. This is your Weight of Goods, otherwise known as the WOG. This weight will be needed in later steps and you absolutely will not remember. Write it down.
Wet out your goods. If the fabric has never been washed, you can run it through the washing machine on hot - this will get out some obvious stuff, plus thoroughly wet out the fiber. If you are not coming from a washing machine - put your fiber in a big bucket of water and let soak until deeply truly wet. Minimum an hour, preferably over night. BTW I would not put cotton yarn into the washing machine...
Fill up the scour pot. I fill up my big pots using buckets. Leave enough room for your fabric. Note the quantity of water used. Preferably in liters, You need to know the volume of water you are going to be using.
Figure out weight of soda ash. I use a solution of 1-2% Soda Ash with my acidic tap water. This works out to a roughly a heaping teaspoon per liter of water. The goal is a pH around 10. Weigh this out into a containers. 1% if pretty clean especially used cloth that has been washed many times, and 2% for new and or stiff cloth. (Old sour cream containers shine for pre-scaling your powders.)
Dissolve the washing soda. Put on a kettle of water to boil. Meanwhile put a bit of tap water into a glass measuring cup and pour in your washing soda - stir up. Always add powders to liquid, not liquids to powders. Pour some boiling water into your cup and stir until soda ash is dissolved. Add this solution to the big pot. You want a pH of around 9-10. It will feel slippery. *Safety note: goggles are good if you don't wear glasses.
Slosh in the synthrapol. I also usually glug in the sythrapol by eye. Around a tsp per 500g of cloth. Stir it all up.
Enter your goods- as you put them in try to avoid twisting the material. Sort of fold it in. Also be mindful of trapping big air bubbles. Remember learning that you could turn your wet jeans into a floatation device if you fall overboard?* Anyway wetted out cotton can hold in a surprising amount of air. Those air pockets will not be scoured.
Boil and Trouble- Bring to a boil, use the lid. Once it is up to temperature turn down to a simmer for 1-2 hours. Let cool in liquid. This can take quite a while. Now some may say that you ought to remove the fiber right away - this always seemed like a good opportunity to get scalded to me. I let it cool down over night.
Rinse well. After it is cool enough to touch take out fibers and rinse really well. I put a bucket next to the pot on the counter and transfer the fabric to it using gloves. To do the actual rinsing I use my washing machine- because my front loader can do a better job with less water than I can by hand. At this point either dry till later, or move on to mordanting.
Neutralize the Scour liquid and dispose. Take the pH of the big pot of brown ducky scour water. Glug in some vinegar until the pH is closer to 7. Once it is tamed I use a syphon to drain the pots into the sink. By first filling the syphon hose with water, blocking off the ends and then immersing one end into the pot of dirty water, and the other down into the sink. No sucking involved.
Repeat process if needed. If the liquid was super gucky- lots of waxy stuff for instance, you may wish to repeat the process again.