MORDANT MONDAY: Tips On Temps For Mordanting Fibers

We get mordant questions all the time at Botanical Colors so why not create Mordant Monday??? Got mordanting questions? Email [email protected]

YOU ASKED: Does your wool gauze need to be scoured before I mordant it?

KATHY ANSWERED: I do not scour the wool gauze as it’s so sheer and fine and it seems pretty clean. It takes the dyes exceptionally well with a mordant only.

YOU ASKED: Which type of mordanting do you think ensures color fastness?

KATHY ANSWERED: Color fastness is a function of the dyestuff and the mordant, not the mordant alone. If you dye a mordanted fabric with a fugitive color, you will still have problems with colorfastness. Mordanting with alum is considered a good choice for ensuring colorfast results.

YOU ASKED: Can you please go over the ideal temperature ranges for scouring and mordanting of various fiber types? I feel like I see conflicting information about which fiber is best mordanted at lower or higher temperatures.


Plant fibers: Mordant at 110 F or lower (hot tap water or even lukewarm). Aluminum acetate will form particles if it is heated above 140F.

Silk: I have always mordanted silk hot (160F), but The Art and Science of Natural Dyes says that heat mordanting can be damaging, so I now mordant cold using cold water from the tap.

Wool is typically mordanted hot (180F) in order to have the mordant quickly penetrate the scales of the wool fiber. It is possible, however, to mordant cold and mordant longer. For example, a hot mordant may take about 45 minutes, but a cold mordant will take 2 days or longer. We will often mordant wool by starting with hot tap water and aluminum sulfate, and then let the entire mordanting bucket cool. Then we hold it in the mordant solution for 2 days and start dyeing then.

We are now carrying a cold water mordant for wool called Aluminum Triformate.  It is easy to use because you create a container of dye and then add wool yarn or fabric to it and let the fibers soak.  There is no need for heat, but overnight soaking gives deeper colors, and rinsing the fibers before dyeing seems to create a beautiful rich color.  We have complete instructions here and I also presented the mordant and my experiments on Feedback Friday.