Washing soda is a type of additive. Additives (also called assistants or fixatives) can change the color of the dye by making the solution either more acidic or alkaline. Last year I used washing soda to turn my coreopsis dye from orange to almost red. It was such an easy method to make two colors with one plant, I wanted to see how washing soda would affect the dyes I made with acacia and oxalis flowers.
Washing soda can be found at most grocery stores in the cleaning section. (Don’t confuse washing soda with baking soda. ) Ammonia is an alternative to washing soda. (I haven’t tried it because I don’t care for the smell. It reminds of washing windows as a kid.)
Warning about using washing soda – a little can go a long way! If you add too much, it can roughen or even dissolve the wool.
My schedule these days feels more hectic/busy/crazy then normal. (How is this possible?) Therefore, my dyes have become mini experiments. My dye pot is the size of a sauce pan.
I used the same process for both the acacia and oxalis:
1. I dyed my samples without the additive and pulled the yarn out once I achieved yellow.
2. I removed the pot from the stove and added 1/8th of a teaspoon of washing soda into dye. (For a normal dye pot amount, I add 1/2 teaspoon at a time until the color changes). The washing soda will immediately change the color of the dye – it’s awesome to watch.
3. I returned the yarn to the pot and let it sit in the dye until the yarn changed color. It’s almost like a double dye.
I showed my kids this process by pouring the dye by into a glass mason jar.
Here are the results!
Myra Made Color 
Science FTW! I love this experiment.
very cool. love the oxalis with washing soda. thanks for sharing these results!
The orange result from the oxalis with washing soda was a pleasant surprise!
I’m a VERY beginner dyer, and the info on washing soda was fascinating! I started experimenting with it in my various solar dye experiments. I had a beautiful purple colored bath made out of the scraps from the purple kale I pulled up from the garden. Turns out, the kale does not do much of anything on its own (at least not that I’ve been able to achieve!), but I split the bath into two jars and added a bit of washing soda to one and it turned forest green! Since the straight kale bath didn’t dye my alum mordanted yarn at all, I didn’t think the kale w/ WS would, either, but I let it sit for a week, just to see. It actually kept a pretty soft mint color when I finally washed it out. I have no idea how long the color will hold, but it was so much fun to experiment!
Laura, I feel like a beginner dyer, too! What a neat experiment – that’s cool the washing soda turned the dye from purple to green. I know that with the mushroom Omphalotus, the dye can be either purple or green, depending on the mordant (alum versus iron) and by changing the pH.