How would you make square fireworks?

I saw some square fireworks this summer and I can’t figure out how they were made. They were really square, and not just lopsided circles. They had very straight lines and definite corners. How in the world could these be made?

For that matter, I’ve also seen hearts, peace signs, and fish sparkle in the sky, and I’m very curious about the science behind the special shapes.

The best I can come up with is having the shell explode, with the stars tethered to a central core, each with a string of a different length so that when they’re stretched out, they make the right shape. But I doubt that these tethers I’ve imagined would be able to withstand the force of the explosion.

Does anyone know how things like this are actually done?

It is simply a matter of how you pack the balls into the shell. I doubt if it is as simple as pack them into a square plane and they come out square - through trial and error the right arrangement could be worked out. A star-diamond packing might come out square.

I assume that it’s a matter of shooting them out with varying velocities so that when they detonate simultaneously they are at varying distances from the center. Noodle the numbers and you can get any shape you want.

You’re all overthinking it. Fireworks are spherical plastic shells fillled with “stars,” which are small, spherical, marble-sized lumps of powder. Different compunds of chemicals yield different colors when they burn.

The lift charge fires the shell into the air and a delayed charge in the center explodes the shell at the peak of its travel, firing off all the stars in all directions and igniting them at the same time.

To get patterns, all they do is pack stars of the same color in the shell in the pattern desired. (All major show fireworks are made by hand.) I assume that the rest of the space is filled with inert stars. See here:

In the picture on the linked site, the inert stars aren’t shown. Just change the three interlocking circles in that picture into a square or a heart or a smiley or whatever, and you’ve got your shaped efftect. Simple.