Some natural dyes are more sensitive than other to changes in pH. Both species of madder that I have been using recently, Rubia cordifolia and Rubia tinctoria (or tinctorum) fall into that category. In this post, I am specifically talking about Rubia cordifolia (RC), which is the species that grows in India and is widely used around the world today, though its historic uses stem from India, Africa, and, later, Europe. I started out with two different batches of RC. One appeared a golden yellow, almost like turmeric, when it arrived. The other appears more of a dark terra cotta color. Since the yellow one was already opened for a…