I have been using a lot of fiber reactive dye on cellulose fibers this summer: tie-dye t-shirts, painting handwoven yardage, shibori samplers, etc. It’s getting cool and damp outside now, where I do my dyeing in summer, so I am wrapping up my projects and putting the dyes and resist tools away. I still have a bit of leftover dye stock and mixed colors in the refrigerator, but not enough to cover a large project. I hate to throw out dye while it is still viable, so I need some small projects to use it up.
To finish off the last of the dye before it goes bad, I loosely wind off balls of cotton, linen or rayon yarn, then put the balls in those plastic mesh bags that some fruit and veg are sold in (cherries, small tomatoes, etc.) The bag keeps the yarn from tangling excessively. I throw the yarn in a soda soak until it is saturated, squeeze out excess liquid, then put it in a clear plastic container (like grated cheese is sold in). I add the dregs of dye stock and water to cover it. I put the lid on and leave it 24 hours in a warmish place. Every so often during the first few hours, I swirl the container around to make sure the yarn is completely submerged and the dye liquid can penetrate to the center of the ball.
Winding a loose ball from a cone of cotton yarn. Soda-soaked yarn ball secured in a mesh bag. Yarn ball immersed in leftover dye and sealed in a plastic container.
The next day I rinse the yarn, starting with cool, then gradually warmer water. Finally I soap it in hot water and rinse again, all while it’s still in the mesh bag. The agitation from washing does unravel the yarn a bit, but not enough to tie itself in knots. I hang the bag on a clothesline to dry, usually over another night.

When the yarn is dry, I wind it back into a ball and add it to my collection of colorful yarn remnants, which will eventually wind up in handwoven towels, placemats, scarves, etc. The coloration of the ball is not even, varying in intensity from lighter on the inside of the ball to darker outside. There are also little white, undyed areas where the yarn was touching itself while wound in the ball. Not only do I find this color variation NOT objectionable, I admire and value it. It is another source of delight in seeing unexpected color happen!