Sorta Kinda Lab Report: pH Dependency on Dyes

I decided to do one of the labs that was presented in The Chemistry of Natural Dyes by Dianne N. Epp. The lab tests out what pH levels have on the colorfastness of a dye. Since, I probably shouldn’t post all of the lab information on here, this post will focus more on the results.

The two natural dye sources I decided to test with was onion skins and red cabbage. Funny side story. I went to the store to get onion skins. I got a bad and put one onion in. Then I decided to go treasure hunting through the box that held the onions for onion skins. After being satisfied with the quantity, I went to the register to pay for it. She was really puzzled and was searching for the onion under all those onion skins. She then ripped the bag open and said, “Oh you don’t want that”. And I was thinking NOOOOOOOO. She was extremely confused why I would want it.

So, back on topic. I got all the equipment I needed and boiled the materials. The onion skins had a nice pleasant, subtle smell. The color started to come out as soon as I put it in water. With more boiling, the color became darker and more opaque. I did the same with the red cabbage. That however did not have a pleasant smell. And the color took a while to come out. After the boiling was done, it was super dark purple, almost a black.

I split the dyestuff into three breakers, one for an acid solution, a neutral solution, and a basic solution.Then I put pieces of yarn into each beaker and boiled them for a little bit. After that I rinsed them and laid them out to dry.

Something interesting happened. When I put ammonium hydroxide in the onion skin dyestuff, the color became darker. (If you were wondering, yes I took proper precautions to deal with ammonium hydroxide). However, when I put vinegar and ammonium hydroxide into the red cabbage solutions they both changed colors drastically. I was pretty confused as to why. I went online and found out red cabbage has a natural pH indicator! There are these chemicals that are found in other plants as well called anthocyanin (flavins). You can explore this chemical more by using this article.

As expected, the onion skins binded to the wool with the acidic solution and the neutral solution and not the basic solution. Something that really confused me is the fact that the dye didn’t bind to the wool when the dyestuff was red cabbage. When I went to rinse the wool pieces, I was shocked when the color came right off. After some searching online, I found out that’s what should happen. The experiences of other knitters/crocheters say that red cabbage isn’t color fast, even if you use a mordant.

My next experiment will be to test how mordants affect the color and colorfastness.

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One thought on “Sorta Kinda Lab Report: pH Dependency on Dyes

  1. Pingback: The Sorta Kinda Lab on Mordants This Time « Tales of Steven

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