Source: Blog – Alliance for American Manufacturing
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A union lies at the heart of Chicago’s iconic green river, but the dye’s chemical origin story is murkier.
Every March, the world turns green — at least for a day. From green-tinted pints to emerald-lit landmarks, St. Patrick’s Day is a celebration of Irish heritage, revelry, and, of course, the color green. But behind the sea of green that floods parades and pubs lies a deeper question: Where do these dyes actually come from?
Chicago’s annual dyeing the river green is one of the most popular St. Patrick’s Day traditions. Deeply rooted in Irish heritage, the city relies on its union brothers and sisters to make the transformation happen. Two motorboats handle the distribution — one dumping the dye while another stirs the water — resulting in a vibrant green river within minutes. All of this takes place in under an hour, while thousands gather to witness the magical “leprechaun dust” and kick off their celebration.
The River | Carhartt x Guinness
The formula used by the Chicago Journeymen Plumbers Local 130 remains a well-kept secret, but the tradition began as a way to detect pollution. Originally, the dye was fluorescein, but due to environmental concerns, the city switched to an eco-friendly, plant-based powder in 1966. Today, the dye starts as an orange powder and transforms into a neon emerald green when it hits the water. But just how “eco-friendly” this dye truly is remains a question. While marketed as plant-based and non-toxic, the long-term effects on waterways remain unclear.
The Illinois EPA insists it’s safe. “The dye used is a food-grade dye also used in medicine… Illinois EPA found that at the concentration used in the Chicago River, it is completely non-toxic,” the agency said, per Niche Canada.
The green dyes that color our food, fabrics, and festivities are everywhere on March 17 — but pinpointing exactly where they’re made isn’t so easy.
One of the most well-known food-grade dyes is FD&C Green No. 3 — a synthetic color approved by the FDA for use in foods, cosmetics and pharmaceuticals. This vibrant green dye is used in everything from cupcakes to shamrock shakes. But here’s the catch: the specific manufacturing locations for FD&C Green No. 3 in the U.S. are not publicly disclosed. That means we don’t actually know where it’s being produced — or if it’s even made in the U.S. at all.
For those who prefer natural alternatives, some plant-based dyes exist. Spirulina, a blue-green algae, is a popular natural green pigment used in candy, smoothies, and other foods. In the U.S., Spirulina is primarily manufactured in California and Hawaii, where the warm climate and abundant sunlight create ideal conditions. Other natural sources, such as chlorophyll extracted from leafy greens, are also domestically produced.
While it might be easy to take color for granted, the dye industry plays a significant role in the U.S. economy. Many food and industrial dyes are produced in American factories, supporting jobs in chemistry, engineering, and manufacturing.
So, as you raise your glass this St. Patrick’s Day, take a moment to appreciate not just the hard work of the Chicago plumbers and the factories around the country that produce the dyes that color our world.
Sláinte!
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