I prefer to use unwashed fabric. When I wash any finished project the first time or two I add a Shout Color Catcher sheet to the wash. It catches any bleed of dye from fabric. I enclose a Color Catcher sheet in an envelope pinned to any project I give away with instructions to add it to the wash the first time it's washed.
If I need to pre-wash fat quarters I use my salad spinner and mild detergent to wash each fat quarter by itself. It is gentle and the right size to wash and rinse a fat quarter as needed. I wash, dump the water, and rinse at least twice with fresh water, agitating for a couple of minutes with each new rinse.
I'ld rather use fabric that has been washed. It's softer and I can control it better. Plus it gets rid of all the icky 'cides, pesticides fungicides.........
gini in north idaho
I also like to prewash and then use sizing when I press the fabric.
Pat--"Keep Calm and Carry On"