Question: What’s the hardest color to produce in fireworks?
Answer: Blue, which is produced using copper chloride. But that compound is fragile: it only glows blue within a narrow temperature window, and fireworks typically burn far hotter than the roughly 2,200 degrees Fahrenheit at which it breaks down. Pyrotechnicians have to carefully balance the chemistry to keep the flame hot enough to produce blue but cool enough not to destroy it, and despite centuries of work, we aren’t quite there yet. Watch this weekend’s Fourth of July fireworks, and you’ll see that blue is by far the rarest color used.
