My experience dyeing cotton roving depends on the thickness of the roving.
Manipulating it through all the rinsing is a challenge. I use mesh sweater bags
and baste/sew the bag like a donut - smaller circle/oval in the middle of the roving
and another 1" or 2" outside the roving. With enough room between the center and
outer circles, the roving has some room to move around but not so much room to fall
apart. This also makes it easier to move the roving in/out of the dye/water and makes
it easier to rinse. I spin out all my cotton in a top loading machine - DO NOT ALLOW
IT TO AGITATE. JUST SPIN. For thin roving I make smaller bundles and divide the
sweater bag into smaller quadrants.
The soda ash will kill the dye. Move the roving around a lot in the first 2-3 hours for more
even color. I let the roving sit overnight (which can create darker color on the bottom).
Don't rinse out the soda ash before testing an area to see if it is dark enough. If it isn't,
change the water, add more soda ash, and redye it -- again moving it around a lot in the
first 2-3 hours. If you add too much dye, the dye binds to the water instead of the
fiber. You are better to add more dye in stages than add a lot of dye up front hoping
to get a darker shade.
I also agree that it is MUCH easier to dye yarn than fiber.
Paula Burch at pchurch.net
offers a ton of good advice about
dyeing anything you might ever want to dye.