We get mordant questions all the time at Botanical Colors so why not create Mordant Monday??? Got mordanting questions? Email [email protected]
YOU ASKED: I just ordered both logwood and weld and want to get purple and green on wool yarn based on this information on your site. Do I need to do some pre-mordanting with alum? The website has the intriguing recommendation to use a bit of soda ash with neutral water, to get a better purple. Does this mean an acid pre-mordant would not be advised? It’s hand spun wool for warp so would be better slightly acidic rather than too basic, for wool strength.
KATHY ANSWERED: Please mordant with aluminum sulfate but do not add cream of tartar as tartar will shift the color to more of a brown and in some cases, other acids will shift logwood to an orange shade. The purpose of the logwood in this recipe is to tone the weld to the point where it reads as a green, so you don’t need to enhance the purple shade with soda ash. If you end up using soda ash, you may not really achieve a green shade and get something that is very brown-gray because the logwood will overtake the weld color.
You can also get a slightly different “green” shade with weld combined with a small amount of iron and it will read more of a sage green.
Conversely, when you want to enhance the purple in logwood, avoid mordanting using cream of tartar as you will end up with a brownish gray shade that’s not really purple at all. If the purple color is not very deep and rich, you can add a very small amount of soda ash (0.25% or less) to bloom the color. The pH should be very slightly higher, but still under pH 8. It should not have a negative effect on the wool.
Have you read Making Green with Logwood and Weld? You should!