Ocean acidification isn’t something that most folks lose sleep over. As a side effect of climate change, it doesn’t present a striking image the way a crack in the Antarctic ice shelf or a hurricane-battered coast might. But some problems need to be seen to be believed, so David de Rothschild, founder of the lifestyle brand The Lost Explorer, and Lauren Bowker, the alchemist-cum-designer behind The Unseen, took it upon themselves to draw out the visually indiscernible. They accomplished this feat by devising a special kind of T-shirt, one that changes colors in response to a water’s pH. No toxic chemicals were used to create the effect: just cabbage. Lots of cabbage.

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De Rothschild and Bowker dyed their cotton-and-hemp tee using red cabbage, a leafy green that is rich in a class of water-soluble pigments known as anthocyanins.

Anthocyanins respond to changes in pH by cycling through a spectrum of hues, which range from red-pink to blue-green.

Related: Color-changing syringes can save the lives of millions

“Red cabbage juice contains anthocyanin and can be used as a pH indicator,” Bowker explained. “It’s red, pink, or magenta in acids, purple in neutral solutions, and ranges from blue to green to yellow in alkaline solutions.”

Changes in the pH of water can happen for a raft of reasons. The more carbon dioxide we spew, the more carbon dioxide the oceans absorb. And since some of the carbon reacts within the water to create carbonic acid, the more acidic they become.

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Sulfur-dioxide and nitrogen-oxide emissions from factories, automobiles, and electric power plants contribute to acid rain, while certain detergents can cause wastewater to become overly alkaline.

“So the T-shirts, by changing color, are a really good way of figuring out the state of the local water,” Bowker added.

Related: Beautiful Collision tableware uses red cabbage dye to create unexpected pigments

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The duo didn’t design the shirt to shame people. Neither are they under the delusion that a color-changing garment will save the world.

“I like creating experiences that disarm people because if it’s insane, magical and unexpected enough, they might feel safer about asking questions. It’s this convergence of art and activism and creativity and design. It hopefully isn’t telling people what to do,” de Rothschild said. “T-shirts have always been a billboard to say something. In a funny way, the T-shirt doesn’t need to say anything in this instance. Products won’t change the world, people will! What you do as an individual that matters.”

+ The Lost Explorer

+ The Unseen

Via Dezeen