One of the biggest complaints about hand dyed fabric is that it's not color fast. Many people are wary of using it because they are afraid that the colors will run and ruin their entire quilt. Honestly, it's a reputation that the hand dyed fabric industry has earned.
Here are some hand dyed fabrics that I purchased several years ago. To test them I soaked them for a minute in hot water and then spread them on a paper towel to dry. I used a brayer to press the fabric against the white paper towel and then left them to air dry. All 3 of them ran. Even the one on the bottom ran some, you can see a few purple dots on the towel (click on the photo to see it larger). This is why people don't trust hand dyed fabrics. (Of course, it happens reasonably frequently with commercial fabrics too and that's why I prewash every single fabric that I buy.)
I have a friend who bought some hand dyed fabric from a very well known dyer and the colors ran when she pressed her finished quilt with a steam iron! It was a wall quilt and the dyer specifically sells the fabric for art quilts (not to be washed) but she didn't expect that even a steam iron would cause the dyes to run. In my early days of dyeing, before I started selling my fabric, my own fabrics ran. One spectacular example was a red, white and black baby quilt that turned red, pink and black in the wash.
When I started selling fabric I knew I had to figure out how to process my fabric so it could reliably be used in quilts including being paired up with white fabric.
Most of the dyeing literature tells you to rinse the freshly dyed fabric until the water runs clear and then to wash the fabric in very hot (140F) water with detergent to remove all excess dye. Most people turn their water heaters up to 140 and go with that. The problem is that once that water hits your sink it's no longer 140. Now, I don't know if 140 is really a magical number but "exceedingly hot" is magical. I also have found that a LONG exposure to water is also key. A washing machine only leaves the fabric exposed to the water for about 20 minutes.
Some day I will do some testing to determine which of these steps are key, but for now I will share my own process for getting color fast hand dyed fabrics.
After my fabric has batched I first rinse quickly under running cold water to remove the excess soda ash. As I rinse it I pile up the wet fabric in one or both of these sinks filled with cold water. I process all colors together from this point on.
Darks and lights, blacks and yellows.
After the fabrics are rinsed I add detergent and pour BOILING water over the fabrics.
I leave my fabric soaking in a sink of cold water until the boiling water is ready. Then I drain it, add the detergent and then pour over the boiling water. Yes, we take pots of boiling water to the basement to pour over the fabric. I make sure there is a high ratio of water to fabric. I wear insulated gloves to agitate the fabric in the hot bath then cover it with plastic lids and weight the lids with pans of water. In this step I want to make sure that every single inch of fabric is under water.
I let the fabric sit in this water at least 12 hours. You can see that the water is very dark here. It was even darker 12 hours later. I will do some testing someday, but it seems that the time exposure to water matters as much as anything. I swear it seems that the fabric "burps" out all of the excess dye at some point during the soak. The detergent seems to keep the dye from migrating to any other fabric in the batch. I have never had dye migrate from a dark fabric to a light one using this process.
After the fabrics soak for 12 hours, I the run them through a full wash cycle in the washing machine without soap. Basically it's getting a hot rinse and a cold rinse.
This may seem like a long process but it actually uses less water and time than standing at the sink rinsing every single piece of fabric "until the water runs clear".
I periodically test my fabrics to make sure my process is working fine. I wanted to test the fabrics for this month's palette especially since I have been showing a lot of quilt designs mixing these fabrics with white.
I processed these exactly the same as I did in the first photo. In fact, I did them at the same time. You can see that not one tiny bit of dye stained the paper towel. I will combine these fabrics with white with no problems.
That's why I am anal about how I process my fabric. I dont' want them to ruin your quilt and I don't want them to ruin my quilts!
Note: Please see this post for some additional information.