I’ll wash anything but silk and outdoor fabrics like Sunbrella. Honestly. I’ve washed Black Watch Pendleton Wool, old wedding gowns, and tons of vintage upholstery fabrics over the years. Most of them went right in the drier.
Sometimes, washing will give old fabrics an interesting texture. Like the 70s geometric below. It went into the wash looking a little “bad motel”, but came out looking almost like a batik. Much better.
Another reason to wash–I want my Kiki’s Rewind Designs to be sturdy. If a fabric can’t stand up to washing and drying, I certainly don’t want to use it in a garden apron or heavy-duty bag. These things are meant to get dirty (and clean again).
Front-loading machines are best because they have a gentle action compared to top loaders. They also handle bulky yardage better. Water savings is another big plus.
I wash on the bulky cycle. And if you think a fabric might fade, wash it alone. Ethnic fabrics, plus old American denim that’s never been washed will sometimes bleed dye.
RE detergent: All has a new product out that I’m getting good results with: A Free and Clear liquid with Oxy.
Stains are a whole different post– I usually fill up the bath tub with a very strong Oxy powder solution and soak things overnight. Just make sure to dissolve the oxy powder before adding fabric.
But if you’ve got a better way to handle stains on old fabrics, please share. Like I said–a whole different post and I’d love some fresh input from other fabric lovers.