I said I sort my fabric for pre-washing, but was just wondering outloud why I bother.
Once they are sewn together they are all going to be washed together, right?
I do think the separated colors for pre-wash will diminish the running of darker colors into the lighter colors.
As a side note; I was prewashing a red and white print with a solid white that was to go with it. The red and white stayed like it was printed, but the white piece turned pink. I soaked that one in Oxy-Clean and it took the pink out of it.
This is for a garment, so I think I will try washing them together one more time before making up the garment (unless I can live with a pink trim).
Joyce

Prewashing fabric does more than control fugitive dyes and control shrinkage: It also removes a whole slew of fabric conditioners. Some conditioners interfere with the way fusible products bond; some are sizing that make thin or loosely woven fabric feel more substantial; some conditioners make a soft, short-staple cotton feel smoother and hide the fact that its threads are inherently weak and that the fabric will pill and wear out quickly. I have found, after washing a new fabric that seemed of reasonable quality, that it turned out to be very inferior. Sometimes I will choose not use this fabric in my quilts at all. Sometimes I will just choose not to use it for binding, where I want to use a stronger fabric.

In general, I find prewashing gives you a lot of useful information about the actual quality of the fabric you have bought, and helps you make choices about how to use it: in an heirloom quilt? in a baby blanket that will be washed frequently? In a wall hanging that is not likely to be washed at all after it is hung?

I think it's important to get the sizing out of fabric before washing it. First of all, I can't stand the smell of the sizing, nor the feel of it. You can't be certain that the threads of the fabric have been aligned properly by the manufacturer. Also, it's really important to separate colours-I've avoided real disasters that way.Washing, then stretching the fabric if needed will help your project. When drying the fabric, take it from the dryer before it's bone dry--then you can adjust it as necessary. I press the fabric using a light spray starch. For newbies, there's a difference between pressing and ironing. Pressing is a light, straight up and down motion-not swirling the way you'd press a shirt. This prevents distortion of all your hard work!
I hope this helps.

if you stretch your fabric before you cut and piece with it, you run a very real risk it will revert to its natural shape as soon as it's washed again, thus pulling your block back out of whack - even after it's been quilted. i would discourage that practice and suggest, instead, blocking the damp fabric as you would a sweater. that is, gently smoothing and shaping it, (but not forcing it past its natural limits), then let it dry on its own. to make sure it will stay that way, wet it again with a spray bottle (without moving it) to see what happens to the shape. if it retains the shape, use it as is. if not, either learn to love its whacky warf and weft or save it for a crazy quilt.

i apologize for being so picky and overly obsessive about semantics, but these are important details.

a less important, but equally picky, detail: spray sizing usually doesn't gunk up and get flaky, even if you apply a fairly heavy coat. spray starch sometimes does. (don't ask me how I know that. too much confession may be good for the soul, but it beats the heck out of my ego. LOL)

This is for Joaneau who asked how to control fraying when she prewashes her fabrics:

Yup- agitator washers can do a job on some fabrics. Batiks seem much less prone to this than others. If your machine has a "delicates" or "gentle, fast" setting try that. It does help. I also wash my fabrics in those zippered mesh laundry bags (unfold the fabrics so the water will penetrate!), especially for fat quarters which ravel from three sides! Fabric is getting too expensive to lose significant amounts in the wash!

Also consider keeping a scissors near by. (I hang mine on a cup hook screwed into the wall next to the washing machine, labeled "Laundry Room"). Trim the ravels and knots and untangle the fabric before it goes into the dryer. This lets the fabric relax and reshape and it is so-o-o much easier to press and fold later. Good luck!

Thanks Marsh Queen for your info. You all have many good ideas. I know it will take many different trials and errors, especially for a beginner, but I will get there sooner or later :)

In my younger days I used to work in a sewing factory. One place I sewed all the pockets on blue jeans and another I sewed the cotton crotch lining in underwear. By the time the end product actually goes in a box and shipped out it has been handled by maybe 30 or more people. It's been sat on, dropped in the floor, drinks spilled on them and who knows where else it's been. ANYTHING I buy gets washed before I use it. So there's another reason to prewash. OTHER PEOPLE'S GERMS

Debbie - I have a friend who has worked in the fabric business for over 40 years and her fingernails are terrible - thin and cracked - and she said she thought it was from handling fabrics and the sizing put in it. Don't know if she's right but it sure sounds possible.

I'm new to quilting too, started in January of this year. But a friend who has been quilting for years told me to just unfold your fabric, put it in washing machine, use just warm water and your usual laundry detergent but just wash it for a minute, then let it rinse, and put it in the dryer. Then it usually needs to be ironed before cutting. Of course, you will cut off the frayed ends when you square it up. Good luck.