On Saturday, they will be spectacular bursts coloring the holiday sky above the Delaware River.
But Thursday, they were just ice-cream-cone-shape shells loaded into fiberglass tubes, waiting to be wired and sealed with things you'd find in an ordinary kitchen - aluminum foil and rubber bands.
The elaborate fireworks shows scheduled for 6 p.m. and midnight at Penn's Landing on New Year's Eve are over in mere minutes, but they take months to plan and days to set up. Prep work began Tuesday.
Ken Furstoss, a show producer for the company responsible for Philadelphia's shows, will be the guy holding the firing board that makes the whole shebang pop. Thursday, he stood in a tangle of orange wires on a barge anchored at the Navy Yard, checking connections and supervising several pyrotechnicians loading the explosives.
Working for days in the cold with no gloves - the workers needed their fingers free to handle the delicate wires - can be tough. The payoff is more than worth it.
"We fill the sky," Furstoss said. "We paint it with a scene. I love the thrill factor, hearing the crowd."
Michelle May, a Haverford Township special education teacher and part-time pyrotechnician, will be in New York on Saturday, working a show in Central Park.
But Thursday, she was also on the barge at the Navy Yard, making sure shells got plugged into their proper spots for the Philadelphia shows.
"A lot of people probably wouldn't want to do this," she said of the intricate work. "Fifteen minutes and it's over. But I love giving people a thrill."
Naturally, the pyrotechnicians are adrenaline junkies.
Furstoss got hooked on the idea of setting off fireworks for a living when he flew the president of Pyrotechnico, the company based in New Castle, Pa., that he now works for, to a meeting.
He sold his aviation business and joined Pyrotechnico, which puts on 2,500 shows a year, many during the July Fourth and New Year's seasons.
It's an especially busy week for Furstoss and Pyrotechnico in Philadelphia. In addition to the two New Year's shows, he's also responsible for shows at the Eagles game and the NHL Winter Classic.
But with a forecast for clear skies and temperatures above freezing, even overnight, Saturday's shows should be a breeze, Furstoss said.
"We've shot in pouring-down rain," Furstoss said. "We've shot in blizzards."
In all, the Philadelphia New Year's Eve shows will use 5,000 shells ranging in size from three to 10 inches.
Philadelphia's New Year's Eve shows will use Mediterranean-style firing, with shells firing from multiple positions. Most of the fireworks will detonate 350 feet in the air, though some are designed to go off in the water.
Though people set up the fireworks, computers are integral to the process. A computer command ultimately detonates the pyrotechnics; a soundtrack runs from a remote hard drive.
"It's very high-tech from what it used to be 30 or 40 years ago," Furstoss said.
Still, Furstoss and the other pyrotechnicians are well aware of the physical power of what they're working with.
A 10-inch shell will shake the barge and make the water around it ripple.
And Furstoss is looking forward, as he always does, to his front-row seat.
"If you were on the barge when the shells were being set off, you'd be looking down, not at the sky," Furstoss said. "The explosions are amazing. It's like a war zone."
Though he's never had an accident during one of his shows, Furstoss acknowledges preshow jitters, every time.
"Right before the show, when you're on pre-roll, when the computers are talking and everything is set to go, you can't wait for that first shell to go off," he said. "You hold your breath."