Prism99

You can hand wash them using Retayne to set the dyes, or using Synthrapol (which suspends unset dye particles in water so they can be washed away instead of settling into the whites).

Test colorfastness by dipping a corner into a glass of water. Look for dye release into the water. Also rub the wet area with a white cloth to see if any dye is taken up by the white cloth. If the fabrics pass both of these tests, I would hand wash in Synthrapol.

Synthrapol and Retayne are widely available in quilt stores or online. Amazon has Synthrapol; not sure about Retayne.

You can Google for more information, but here is one website I found:
http://www.quiltbus.com/retayne.htm

Holice

if they have not been washed, which the sacks probably were, washing handles the shrinkage. Always to be safe Usually wetting and pressing water out and ironing takes care of the shrinkage.
They most likely were washed to get the flour or sugar or grain out of them. Most that I have don't continue to run color but better to be safe.

Luv Quilts and Cats

Thanks for all of your ideas. They are really helpfull. I'll let you know how it turns out and post pictures of the blocks when done.

Olivia's Grammy

When I buy feed sacks I run them through the washer on hot with bleach to get the 50 years of stain out of them. It really brightens up the colors. Of course you can't to that with a 5" square. Try swishing them in a bowl or basin with what ever you wash your clothes in.

craftybear

thanks for all of the comments, I learn something every day reading this message board!

You quilters are awesome!