Desizing fabrics before dyeing or sewing

Bolts of fabric waiting to be used in 19th century period pattern projects at UNC-Chapel Hill

It's happened to all of us: you buy what looks like the perfect fabric yardage for a costume from an online vendor, and when it arrives it's got that heavy-duty crisp OMG NEW! sizing that gives it too crunchy a hand. Sadface.

Maybe you need to soften the hand of the fabrics for the purposes of making a costume that's supposed to look lived-in and not crisp-tastic. It can also be a big issue for dyers, as fabrics with sizing in them will often dye irregularly or with undesirable gradations.

But, fear not--there is a speedier solution than "wash the yardage 3098520985 times." It involves a bit of detective work on your behalf though.

Basically, there is not just one type of sizing, so there's not one desizing process that always works. Different fabrics, fibers, and weave structures require different types of sizing at different points in the production process. Sometimes the fiber is sized before the textile is woven or knit. Sometimes the "sizing" is actually a finishing process applied after the yardage exists or the garment has been sewn.

There's not a quick and easy test to determine what's making the fabric crisp, and unfortunately a process which removes one type of sizing efficiently may not have as good of an effect on another type of sizing. So, let's look at ways to remove some common stiffening/smoothing agents

PVA

A lot of modern fabrics are sized with PVA (aka PVOH or polyvinyl alcohol, which is basically white glue). It's technically water-soluble, but can take multiple standard domestic launderings to totally come out. If PVA sizing is particularly tenacious, adding a very small amount of sodium hydroxide (NaOH)--aka lye or caustic soda--to your laundry load will help with removing it faster, but it can also act as a breakdown agent, which in fact might be desirable if you want the fabric(s) to look old, faded/distressed, etc. 

Lye is highly corrosive and easily splashed in liquid form, so be sure to use gloves, splashproof goggles, and great care when working with it, rather than just dumping some into the machine carelessly. 

In fact, it'll be a lot safer (and probably easier to purchase, handle, and store) if you use lye soap flakes instead of NaOH solution. Also, maximum agitation and higher heat of the wash bath (above 75F/25C) will help, too. If you have some particularly tenacious PVA sizing, you can even boil the fabric to get it out.

CMC

If your fabric is sized with CMC (which stands for carboxymethylcellulose), that's the easiest to remove--a hot laundry load will usually do it. If you have soda ash or washing soda on-hand for dyeshop purposes, tossing a little into the bath will desize CMC from a fabric even more efficiently.

Acrylic

Acrylic sizing is similar to acrylic paint or acrylic medium--if you've ever used acrylic medium to stiffen yarn or fabric, you've done something similar to sizing with it! Acrylic sizing is water-based and can be removed with a cold or warm cycle and laundry soap..

Starch

Traditional starch is actually often the most difficult to fully remove. Like PVA, it requires high heat and agitation, and will come out quickest if you boost the laundry bath with the enzyme amylase, which is found in some enzymatic cleaners. Detergents with amylase don't always feature the word "enzymatic" in their ad copy, so it pays to read the labels. Often ones that cater to the Green market share will have it as a component--Seventh Generation and Nature's Miracle, etc. (Amylase is also found in saliva, but your coworkers might look askance if you go ask everyone in the company to come spit in your washing machine.) Peroxide bleach will also remove starch, but also tends to weaken cotton and linen fibers so use care if you go that route.

How do you know what something is sized with? 

Unfortunately, there's no way to really find out unless it's printed on the tag or bolt end or whatever. That's okay though--you can figure it out! Here are a few tips to help with your guesswork.

• Starch is typically only used in cotton processing, so if you have a non-cotton fiber, it's unlikely to be sized with starch. Cotton doesn't automatically mean "starch" though--it could be PVA or CMC.
• Nylon fabric is often sized with acrylic sizing. 
• Polyesters are usually sized with water-dispersable synthetic sizes like PVA or acrylic.

In general, when i'm desizing fabric to prepare it for dyeing, i start with a hot laundry cycle, high agitation, and using an enzymatic detergent plus washing soda. If it's still stiff after that, then i start troubleshooting with other methods--lye flakes, hotter bath, even boiling.

Have you ever worked with a fabric where the sizing just wouldn't come out no matter what you did?