The first thing I do is cut my fabric (in this case it is TestFabric 400M) and for gradations I cut them 1/2 yard each.
Then I put them in a bin of soda ash and water. I use PH plus from the pool store as my source for soda ash. It is cheaper and easier to come by. For each gallon of water I use 1/2 c. ash. When I know that the fabric is saturated, I lightly wring out. Anymore than a light squeeze can screw up your elbows if you do it enough. I know that from experience. Let the washer do the work.
Now these 'ashed' pieces are tossed into the washing machine and put on the spin cycle for a
minute or two to get the excess wetness out. If you have lots of this fabric prepared and can't
get to it right away, stuff it into a ziplock and it will be good to go when you can get back to dyeing. As for mixing dye powders for your color, there are a million ways to do it and the process I use took a week of class to learn. It involves measuring by weight rather than container. Whatever way you do it, you start out with the darkest value of the color you have chosen.
For these examples, I have photographed two separate gradations, one burgundy and one green, and so there are different colors in this tutorial. I just didn't want you confused.
I decide on how much dye solution to use and I pour it in a rubbermaid throw away bowl , along with 1/2 cup of warm water, stir them together and add my fabric. As I said before, I always make two of everything, hence the two identical bowls.
I manipulate the fabric, squeeze out the excess dye a couple times, hold the piece up to see if there is any white showing and when I feel like the color is good all over, I leave it alone. All this working the fabrics take less than a minute. Then with each value change, the dye concentrate get's cut in half but it always get's 1/2 warm water stirred in (otherwise it would be too little liquid to color the fabric.
These photos show four of the six colors in a typical gradation. You can see the color get lighter and lighter.
In between getting another value ready I throw the bowls in the micro and nuke each (with lid off; it will come off anyway if you put it on tight) separately for one minute. Then the lid goes on and they are left alone.
Here is how I leave them alone, anywhere from two hours to a day, depending on what I have going on in my life.
Usually when I do gradations, I do four colors at the minimum each day. I figure that I am on a roll and have a mess anyway so........ I have gotten in the habit of spinning out each gradation (in my case 12 half yards) separately first and just putting them in a bowl while I do the others. Because I only spin for a couple minutes, this doesn't take very long. Then I throw all the dyed fabric in the washing machine on the highest water level with Tide and wash in the hottest setting . I do this twice and for most colors that may be overkill but I would rather be safe than sorry. Then I take out the tangled mangle of fabric from the washer and I no longer just rip them apart (they fray and get twisted and all that) and plop them in a dryer. Now I air dry them. I take them out of the washer and untangle and then stack them up on top of each other and put a few deep over the back of a chair. Believe me they are a lot easier to iron this way.
Doing the dryer way, like this, is an ironing nightmare. They are so dry and stiff and wrinkled that you spend twice as much time pressing them and they will need heavy sprinkling too. My way is a zillion times easier, and you press them when they are still damp.