The spectroscope
The gemstone sets the spectrum; the shape only changes the drawing.
Drag across the spectrum, or press [ and ] to step from line to line.
693 nm Line: the R lines, a close pair in the deep red (Cr³⁺), distinct.
Lines identify the coloring element, not always the stone. These are chromium's lines: emerald shows chromium lines too, in other places, and a laboratory-grown ruby shows exactly these.
A longer path darkens every line and band; a shorter one shows lines a dark stone hides.
White light passes through the stone and into the slit. The prism or grating spreads it into its colors, violet to red; wherever the stone absorbs, that part of the spectrum goes dark.
Both rays measured: GIA's published Cr3+ cross-sections (Dubinsky, Stone-Sundberg & Emmett 2020), at the chromium content of a natural ruby from Thailand (G.R. Rossman, Caltech).
The same measured spectra give the two colors in the Dichroscope.
What a spectroscope shows for each gemstone
| Gemstone | What the trade sees | This model, 5 mm in lamp light |
|---|---|---|
| Diamond (shown above) | Colorless: none. Yellow (Cape): a line at 415.5 nm, with weaker lines at 478, 465, 452, 435 and 423 nm | No lines or bands |
| Moissanite (shown above) | None in the visible; some stones absorb toward the violet | No lines or bands |
| Cubic Zirconia (shown above) | None | No lines or bands |
| Ruby (shown above) | Chromium: a close pair at 692.8 and 694.2 nm (often bright), weaker lines at 668 and 659 nm, a broad band from 500 to 610 nm, lines at 476.5, 475.0 and 468.5 nm, the violet absorbed | Lines at 468, 476, 659, 668 and 693 nm; bands 400 to 442 nm and 490 to 607 nm |
| Sapphire (shown above) | Iron: lines at 450 nm (the strongest), 460 and 471 nm, strongest in iron-rich stones | A line at 452 nm; a band 602 to 700 nm |
| Emerald (shown above) | Chromium: a pair at 683.0 and 680.5 nm, lines at 662 and 646 nm, a partial band from 580 to 630 nm, a weak line at 477.4 nm, the violet absorbed | Lines at 637 and 681 nm; bands 400 to 455 nm and 571 to 642 nm |
| Amethyst (shown above) | Nothing telling: at most a weak broad band in the yellow-green | A band 497 to 586 nm |
The model lists what you can see through a 5 mm path in lamp light, spread by the grating: a line or band too faint to see is left out. Diamond is colorless here (the simulator’s D); a yellow diamond’s lines are not modeled, for want of a measured spectrum.
A model of a hand spectroscope: a straight path through each gemstone, across its optic axis, in lamp light or daylight, with the spectrum computed from measured absorption spectra. It is not a test of a real stone. How the spectroscope is modeled.