Image by Mike Schwarz

In 1971, artist and former activist nun Corita Kent was commissioned to tackle the largest copyrighted work in the world: the freestanding Rainbow Swash gas tank towering above the Southeast Expressway off I-93, overlooking Dorchester Bay under the Hub skyline.

The story behind Kent’s kaleidoscopic landmark, of course, is more complicated than that. For starters, in 1992 the iconic design was transferred from the original tank to its replacement on abutting property. The whole thing intrigues me. And so after years of driving past the monolithic concrete table coaster, currently stamped with the National Grid logo, I took an opportunity to check in on the painters touching up the Rainbow Swash—and to wheeze, cough, and ascend an acrophobe’s nightmare of spiraling iron stairs.

This was no matter of rustling up a few pails of paint and finding someone with brass balls big enough to handle such a mammoth project. The maintenance was overseen by the International Union of Painters & Allied Trades (IUPAT), whose members got to work in June and put the final coat on last week. In all, they were responsible for more than just the preservation of commissioned artwork. They also had to help prevent disaster from unfolding.

“Basically the main purpose is to protect against corrosion,” says Justin Desmond, the Roslindale-based organizer for a local district council of the IUPAT. “It’s important those coatings go on correctly.”

Importantly, base, hardener, and catalyst applications are needed at certain times and for certain temperatures; in the summer, for instance, the tank metal can reach up to 180 degrees. Because of the variations in temperature, all products used for the protection of the tank’s aesthetic and structural integrity have corresponding data sheets to ensure safety measures are met, and to shield the environment in the area surrounding the project.

A sight like the Rainbow Swash is something commuters notice, so it’s paramount that upkeep treatments come from quality contractors. In this case even more than in others, prioritizing cost and cutting corners before tending to high standards can lead to ugly results. Take the infamous tank in West Virginia that for years endured neglect and high levels of corrosion. Despite warnings from the IUPAT chapter there that officials needed to use trained workers, hazardous contents eventually spilled into the Elk River, causing a federal emergency.“All the guys we employ are competent and know what they’re using, down to the organic compounds in the products that get released into the air,” Desmond says.

“What we see is an underground economy [of] projects afforded to the lowest bidder because of bylaws out there that basically say, at one time, taxpayers were convinced the taxes would be lowered by lowering the costs for upkeep of structures like this,” Desmond says.

I go through several security checkpoints before meeting my IUPAT chaperones under the rainbow. After 9/11, tank security was tightened, so much so that California-based photographer James Prigoff was entered into a Department of Homeland Security database of suspicious persons after he was caught photographing the property in 2004.

We tour the grounds, circling the base of the structure, and cross over an empty moat that is invisible from the interstate. I’m told it’s here to safeguard from potential catastrophe; if the liquid portion of the natural gas spills into the brick-lined reservoir, the apparatus will prevent contamination of surrounding waters. A comforting thought considering I live less than a mile away.

On our climb from the base to the 140-foot summit we pass several gruff painters. Some are rappelling from safety harnesses, dangling on ropes at precarious angles over the edge while stroking Kent’s masterwork down to the controversial crevices. Before their reproduction on the new tank in 1992, the stripes were criticized by some due to a rumor that the profile of Vietnamese leader Ho Chi Minh could be seen in the blue swath (Kent, though a peace activist, denied the charge).

Once there, the view from up top is spectacular, panoramic glory. From the recently closed Long Island Bridge to the foliage peppering Dorchester, Boston’s urban sprawl look that much less urban from this vantage point.

The journey down is tough due to the angle of the stairs and the low handrail. But it’s informative, too, as John Doherty, the regional director of organizing for IUPAT, schools me on the vast artistic chops of the crew. They’re trained, he says, to replicate whatever they have to. On this job, that means applying chemicals and science to stave off corrosion and maritime tear, and also employing certain “graffiti-free” compounds. Nobody, says Doherty, is going to leave their own creative mark on the tank.

“Except,” he jokes, “for what [Kent] did, anyway.”