Natural dye recipes are generally done by weight, not volume, so you will see amounts given in grams and ounces, rather than teaspoons or cups. This means that if you are planning to embark on a journey with natural dyes, one of the best tools that you can acquire is a scale. It doesn't have to be fancy - these days you can find a basic digital kitchen scale for 10 to 20 dollars.
The next big thing to know is the acronym WOF%, which stands for Weight of Fibre Percentage. Most natural dye recipes will be given as a WOF%, since how much dye or mordant you need is determined by how much fibre you are planning to dye.
First off, weigh your fibre. (Top tip - if you are dyeing store bought yarn, the label will have the weight right on it - it will be marked 100g etc) Then find your WOF%. All of our bulk dyes have this listed on the back - for example, our Logwood is marked "Use at 10-15%". So if you are planning to dye 100g of fibre with our logwood, you will use 10-15g. If you're dyeing 500g, you'd use 50-75g (500 x .10 - .15).
Now the big question is - why the range? Why not just say 10% or say 15%. Essentially, it's because natural dyeing has so many factors involved, that it's hard to pin formulas down to an exact number. There are so many things that will affect your shade, such as what type of fibre it is (which I went into at length in my last newsletter) and even what season the plant was grown in. Like wine, plant dyes can be very different from year to year - a plant grown in a hot summer may yield more colour than one grown in a rainy one. So a range is given, to give you a starting point, and each individual dyer will develop their own recipes as they gain experience.
In general, the range that is given is for a medium depth of shade. So you may also choose to use more or less dye than the recommended WOF, if you are aiming for a very pale or a ver dark colour. For example, if your goal was the palest of the purples in the photo below, you might begin with only 5% logwood.
All of that said, natural dyeing is like cooking, and there are many styles of dyer and no right or wrong way. Just like cooking, you may be someone who measures their ingredients precisely and keeps meticulous notes. Or you may be someone who adds a pinch of this and a scoop of that, and is happy to experiment and see what happens. And you also get to choose which type of dyer you are! It's entirely possible to natural dye successfully without weighing a single thing. But as beginners, most folks will find it useful to have the jumping off point that a WOF recipe provides.
Finally, whether you measure meticulously can also be determined by what dyestuff you are using. If you're dyeing with cochineal, for example, which is both quite pricey and extremely potent, you may want to be a little more precious with your measuring - using the lower percentage and measuring carefully. But if you're dyeing with goldenrod that you have gathered in the fall, when it is everywhere, you can just fill your dyepot to full and see what happens.
Whatever you do, be sure to remember that the best results often come from experimentation, and to let yourself have fun with it.