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Ways to add a splash of color to your summer

by Bethany Halford
June 30, 2022 | A version of this story appeared in Volume 100, Issue 24


Tie-dye in NY

Julian Silverman is fashioning an unusual collection of New York City’s discarded objects: the Fashion Institute of Technology materials science professor forages waste from the city and turns it into colorants for tie-dyeing. His finds range from organic materials like acorn caps and avocado skins to inorganic objects like discarded rusty bolts from NYC’s subway.

A man wearing a t-shirt with a black and orange tie-dye pattern.
Credit: Pamela Anderson
Shirts and skins: Julian Silverman tie-dyed his thrift store T-shirt using avocado skins and iron.

“I collect rusty metal everywhere,” Silverman tells Newscripts. He rinses the oxidized metal and digests it with acid to create oranges and reds. Foraged acorn caps make lovely brown dyes. He can also mix those solutions with tannins to create a black liquid. The iron from the rust serves as a dye fixative to help tie-dye cotton.

The tie-dyeing project connects green chemistry and environmental science, Silverman says. You can follow his dyeing adventures on Twitter, where Silverman posts photos under the handle @heterocat. He also recently published a paper on a tie-dyeing workshop he developed (J. Chem. Educ. 2022, DOI: 10.1021/acs.jchemed.2c00086).

“We’re taking abundant resources that are around us and also diverting them from a landfill,” Silverman says. “Students can learn that not only is waste useful, but there are things literally right outside your door that you can do fun, interesting projects with.”

Silverman says one of his favorite aspects of the tie-dyeing project is that it is seasonal. He uses acorn caps for brown dyes in the autumn and plants like chicory in the summer to give bright, yellow hues.

Tie-dyeing with natural and found materials isn’t new, Silverman says. “I really took a lot of other ideas I had seen and just made them local.” He hopes other educators will do the same, using their own found objects and local plants to create sustainable dyes.


Ice cream blues

Color-changing ice cream with a blue base color and C&EN in pink.
Credit: Bethany Halford/C&EN
Color me pink: This blue ice cream turns pink when painted with lemon juice.

Back in 2014, Newscripts featured a color-changing ice cream available in Spain. The confection was blue when scooped and changed to pink and purple when spritzed with an elixir. At the time, the ice cream’s inventor was keeping the sweet treat’s color-changing chemistry a secret.

A few years later, Newscripts learned of the butterfly pea flower. This bright blue bud is loaded with anthocyanins that change color in response to pH shifts. The flowers are dried into a virtually tasteless tea that colors cocktails and other beverages. Blue gin, for example, will turn pink with the addition of tonic water.

Butterfly pea was obviously the color-changing ice cream’s secret ingredient, but this Newscriptster’s attempt to make a frozen dessert from the tea yielded a ghastly gray concoction. Alas, homemade color-changing ice cream wasn’t to be on the menu. We’d have to stick with gin and tonics.

But time, the internet, and a search for a topic to fill the second half of this column yielded a 2019 recipe for color-changing ice cream on the maker-friendly website Instructables. The recipe’s author, a chemical engineer named Britt Michelsen, uses a powder made from butterfly pea blossoms rather than an extract from the tea. Good news for vegans: Michelsen also found that a frozen dessert made from coconut milk had a bluer hue and a more pronounced color change than a frozen treat made from dairy cream.

This Newscriptster whipped up Michelsen’s recipe to see if the results were reproducible. The blue hue did change to pink when dabbed with lemon juice, but the tart juice detracted from the ice cream’s flavor profile. Adding a swirl of lemon curd to the partially frozen ice cream was more successful in terms of taste, but the color change was more subtle, with pinkish streaks appearing at the ice cream–lemon curd interface.

Butterfly pea tea can also be cooled to make ice cubes. Add these to lemonade and the refreshing drink will slowly turn pink as the cubes melt—a fun experiment to liven up the kids’ lemonade stand.

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