May 20, 2015
Congratulations— you and your students have almost made it through another school year! There’s still time for some hands-on labs and now, more than ever, is the time to tie in some fun with your lesson.
Tie dying is always a great year-end experiment and as chemists, we want to make it a real bonding experience for you and your students. Not only is it fun to guess which student will end up with the most dye on their arms, students have an opportunity to incorporate chemistry in a meaningful way while creating a nice keepsake.
Memento from my Chemistry teaching days
First, you’ll want to purchase reactive dyes since they are very brilliant and colorfast. They actually bond with the fabric, making the color on the shirt last longer and the chemistry more interesting.
Despite student protest that this is “just supposed to be fun”, tie dying is an opportunity to review concepts of concentration, absorbance and transmittance. With a PASCO Wireless Spectrometer, you can explore the absorbance of the different colored dyes before you start the process of coloring your shirts.
Red dye spectrum showing the expected absorbance of green light.
Blue dye spectrum showing the expected absorbance of red/orange light.
"Purple" dye is actually a mixture of blue and red dyes.
To really engage students in the technique of dying and in engineering process skills, the experiment can be opened up to student inquiry. Some things they could investigate as they try to create more vibrant colors include:
• Comparison of reactive dyes, union dyes and acid dyes
• Preparation and use of natural dyes
• Comparison of synthetic and natural fabrics
• Dying conditions like temperature, time and pH
To explore natural dyes, I created a yellow dye using turmeric, a red dye using beets, a purple dye using blackberries and a blue dye using red cabbage— I changed the red cabbage blue by adjusting the pH of the solution… but that is a story for another post.
Once again I turned to my trusty Wireless Spectrometer, this time comparing similarly colored solutions.
The yellow reactive dye and the turmeric had very similar spectra.
Finally I tested the natural dyes on fabrics, in this case silk (top) and cotton (bottom).
Beets (red), cabbage (blue), turmeric (yellow), blackberries (purple)
The results on the fabric are mixed, but because of the real-world application of science and engineering practices, the student learning is very real. And if nothing else, everyone gets to take home a really cool shirt.
If you have any questions about the types of dyes and the preparation, please email me at firstname.lastname@example.org.
Special thanks to my daughters; my older daughter, whose science fair project inspired this post; and my younger daughter, who enjoyed helping with the extraction and dying processes.