Back then, all they had to work with, was natural dyes: the color varies in the dye lot, based on the wool used, how you put it into the pot, and how much dye you use. It was art, not science. The wool fibers absorbed the dye differently, from one wool hair, to another; the dye was not uniformly distributed within the hot water; it also depended upon how many bundles of wool had been in the pot, previously, which drained the dye batch of color.
Then there is the type of Mordant used (fixes the color in the wool, permanently), which also affects the final color outcome. For Gray dyes, it was common to use iron water (a Mordant, which darkens all colors), or rust water: it will actually darken the wool, permanently, to a gray color, with the shade depending upon how long you "cook" it in the Mordant water, and how strong the Mordant is, in the water. Art, not science.
Modern, chemical dyes, color the wool, with sheer brute force, yielding uniform color, easily, and effectively. They are nothing like natural dyes. Chemical dyes are more affordable, and offer the entire rainbow of colors to choose from; natural dyes are much more limited, and expensive! Fiber groups offer en entire class on dyeing with natural Indigo, alone, as it is very versatile, and useful for a wide tint range. Indigo also has special handling techniques to tease all of the tint ranges it has, out of it.
Precise color control is not possible, with natural dyes. The next time you visit a Re-enactment Fair, spend some time visiting with any wool dyer's you can, to discuss achieving colors. Take a close look at their bundles of dyed wool, on display. You will see variations within the same bundle, which was dyed at once, in the same pot!
Ask them, as well, how the colors wear, over time, in the field (sunlight, mud and rain). Natural dyes are not nearly as durable as modern chemical dyes. It should be quite educational if you can pick their brains for a while.
You can also enroll in a natural dye class, if any are offered in your region. I took such a class with my wife. It was scientifically fascinating, and educational, to learn what plants can be used for dyes, what colors can be achieved with what plants, and insect shells; then there are the Mordants, which fix the colors within the wool… Amazing stuff, really. Cheers!
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