What is a mordant?
When you are about to paint a piece of furniture that has been previously painted, it is advisable to sand to open the pores so that the new paint can penetrate and hold, right? Well, the mordant does something similar with natural dyes in the fibers. From the Latin mordere – “to bite, to sting”, it is a substance that acts by opening the pores so that the dye can penetrate the fiber and thus increase its fixation.
Therefore, the mordant is a substance used to modify the cell wall of the fiber and thus allow the color to penetrate and remain in the fiber over time.
There are many types of mordants, and their use depends on the type of fiber you are going to use, whether it is an animal or vegetable fiber, the dye you are going to use and the technique employed.
Potassium alum is one of the basic mordants in natural dyes and of course it is not toxic, in fact, if you are familiar with alum crystal deodorant, you should know that it is the same, but crystallized.
You can use it mixed with cream of tartar for better results in wool fibers.