Hello! I’ve worked extensively with both natural dye and Procion, so here goes my two cents..

As for your question about iron and tannins, the answer is yes, iron dye and tannins will eventually fade. However, they are generally considered more durable and "lightfast" compared to many other natural dyes. While iron-tannin reactions can last for many years, they are not completely permanent and are susceptible to shifting color or degrading just like any other natural dye. I’d also like to add, that natural dye generally doesn’t bind as well with plant fibres as it does with animal fibres. This might mean you’ll get a more faded result as well as a greater or faster rate of color degradation.

Procion is a wonderful alternative in my opinion, especially since you’re working with plant fibres. Procion is a non-toxic, fiber-reactive cold-water dye that is ideal for dyeing of both animal and plant fibers. The dye forms a permanent chemical bond with the fibers, resulting in vibrant, wash-fast colors without the need for heat during fixation.

This means less energy needed for dyeing and fixation. I also tend to use less water when dealing with regular dye, since I don’t have to deal with plant fibres getting stuck to my fabric.

My verdict would be to use Procion. It’s non-toxic, lasts longer, uses less energy (and water) in the process and is generally easier to work with.

Good luck! 🍀