it's not roving, it's combed top, but since "painted roving" has become the generic term for this product regardless of whether it's actual roving or top, that's how I'll refer to it. It's very pretty, but not quite what I was going for.
In dyeing, the intensity/darkness of your final product is determined by a ratio of dye to fiber, by weight. If you want a lighter color you use less dye, if you want a darker color you use more. Sounds logical and reasonable, right? This relative intensity of color is referred to as Depth Of Shade, and is generally abbreviated as DOS. If you want consistency and repeatable color (e.g. professionals and perfectionists), you will not just toss everything in a pot and see what comes out - at least not without keeping very careful notes!
If you want consistency and repeatable color you will use a formula to tell you what ratio of dye to fiber will give you a certain DOS. The current dyer's standard (as far as I can tell) is to use a scale that generally starts with DOS .25 (very pale) and ends at DOS 4 (as dark as it's possible to get for that color). In immersion dyeing, where you are dyeing everything one solid color, if you want DOS 1 you use a 1:1 ratio of dye to fiber. A DOS .25 would be .25:1 dye to fiber, etc. You then add enough water for the fiber to move freely and "cook" everything at the appropriate temperature until all the dye in the water has been absorbed by the fiber.
With dye painting it's a little different. You have individual cups of dye that you apply directly to the fiber. You place the color exactly where you want it, and have some degree of control over how much the colors blend where they meet. There is also an optimum amount of liquid that can be applied to roving for dyeing. If you use too much, everything blends together a lot more and you have less control. Too little, and you end up with undyed spots where you don't want them.
According to Deb Menz, when you are doing painted roving, you should use double the amount of dye to get the desired DOS. I'm not sure why or how this is necessary, or how much of it is just "fudge factor." I wanted the test roving at the top of the page to be a medium grey, a medium navy, and a dark forest green. Even though I know I did all the math correctly, I ended up with way too much liquid! While she provides good Three Bears examples (too much, too little, just right), she doesn't say "You may not need all the dye you have mixed to achieve this." By the time I had applied the blue, the green, and half of what was supposed to be dark grey, my roving was sopping. I stopped adding dye because I knew this was way too much, and decided to see what I would get with what I had.
What I got is at the top of the page. The grey is still black (not dilute enough), the blue is darker than I was expecting, and they both have pretty much swallowed up the green. Obviously I had more dye than I really needed, and I can't afford to rinse color down the drain for the sake of "fudge factor." I will try this again with some modifications, and we'll see what happens!