ARTIFICIAL WASTELAND · A FLAME-TEST BENCH

The color you see is a wavelength you can read

A red firework is glowing strontium; a green one is barium; a blue one is copper. Each metal salt, heated in the burst, emits light at fixed wavelengths set by its atoms and molecules. Pick a salt below — the color in the swatch isn't chosen by hand, it's computed from representative emission features through standard color-matching functions. Then explore blue's need for careful flame tuning with an illustrative heat slider.

Why blue is the hardest color

Red and green ride on rugged emitters — strontium and barium bands that shine brighter the hotter the flame. A familiar blue emitter is copper(I) chloride, CuCl; copper(I) iodide also produces blue. A blue star needs careful flame tuning to form and preserve its emitter. Published work reports blue emission at 1200–1500 °C, so 1200 °C is no universal cutoff. Red and green also have temperature-sensitive color chemistry.

Select Copper above and drag past the model's illustrative 1200 °C threshold: the spectrum and glow fade, while the glow remains visible with unchanged RGB. Do the same with strontium and the red stays unchanged. This slider only models a fall-off for copper; it does not predict other emitters' responses to heat.

The honest footnote the color charts skip: the reds, greens and blues are mostly molecular emission — strontium monochloride, barium monochloride, copper monochloride — not bare metal atoms. Only sodium, lithium and potassium here glow as clean atomic lines. The spectrum plot marks which is which.

How this page is built — and checked

The wavelengths are real and sourced. Atomic lines (Na, Li, K) are from the NIST Atomic Spectra Database; the molecular band heads (SrCl, BaCl, CuCl, CaCl) are from pyrotechnic-flame spectroscopy (Douda; Conkling, The Chemistry of Pyrotechnics). Every swatch color is computed from those wavelengths by the CIE 1931 2° observer (Wyman, Sloan & Shirley 2013, an analytic fit to the standard color-matching functions). An offline verifier re-derives the model arithmetic and asserts each color lands in its expected qualitative bin, and that copper's modelled luminance falls while its RGB stays unchanged: research/fireworks-colors/verify.mjs, 28 checks. The page and the verifier import the same spectra.mjs, so the color on screen is the color that was checked. The temperature threshold and fall-off curve are illustrative settings, not measured material limits or intensities. Relative feature weights are chosen model inputs. Potassium's far-red contribution is omitted from this simplified swatch.