The Eickhorst spectroscope is a hand-held or bench-mounted diffraction spectroscope manufactured by the Hamburg-based instrument maker Eickhorst GmbH, long regarded as one of the standard tools of the professional gemmologist's bench. By dispersing transmitted or reflected light into its component wavelengths across the visible spectrum (approximately 400–700 nm), the instrument reveals the characteristic absorption lines and bands that allow the identification of gem species, the detection of certain treatments, and, in favourable cases, the narrowing of geographic origin. Eickhorst instruments are particularly well regarded in European gem laboratories for the clarity of their optics, robust construction, and consistent calibration.

Principle of Operation

A spectroscope of this type functions by passing light through or reflecting it from a gemstone, then directing the emergent beam through a diffraction grating or prism that separates it by wavelength. The observer views a continuous rainbow-like spectrum against which dark absorption features — lines or broader bands — appear wherever the stone's constituent chromophores have absorbed specific wavelengths. The Eickhorst design incorporates a slit aperture at the entry port, a collimating lens, the dispersing element, and an eyepiece, all housed in a compact, light-tight barrel. A built-in wavelength scale, visible simultaneously with the spectrum, allows the observer to read off absorption positions directly in nanometres without the need for separate calibration charts.

Construction and Variants

Eickhorst produces both hand-held models, intended for rapid screening at the loupe stage, and more substantial desk-mounted versions that accept a fibre-optic or incandescent light source for higher-intensity illumination. The desk models typically offer a wider field of view and finer slit adjustment, making them preferable for recording faint or narrow absorption features. All models are manufactured to tolerances consistent with professional laboratory use, and the instruments are distributed widely through gemmological supply channels across Europe and beyond.

Diagnostic Applications

The spectroscope remains an indispensable first-line identification tool despite the proliferation of more sophisticated analytical instruments, because it is non-destructive, requires no sample preparation, and yields results within seconds. Key diagnostic applications for the Eickhorst spectroscope include:

• Ruby and red spinel: Natural and synthetic ruby both display the chromium doublet at approximately 692 and 694 nm, together with broad absorption in the yellow-green region; the spectroscope allows rapid confirmation of chromium as the chromophore and can help distinguish ruby from red garnet, which shows a distinct three-band iron spectrum in the yellow-orange.
• Sapphire: Blue sapphire of iron-titanium colouration shows three iron bands at 450, 460, and 470 nm; yellow sapphire may show an iron band near 450 nm; the presence or absence of these features assists in separating sapphire from blue synthetic spinel and blue glass.
• Emerald and alexandrite: Chromium-bearing emerald displays a strong doublet in the red (around 680–683 nm) and broad absorption through the blue-violet; alexandrite shows a similar chromium signature, and the spectroscope can confirm chromium colouration in both species, supporting distinction from green glass or chrome-free synthetic counterparts.
• Almandine garnet: The characteristic three-band iron spectrum centred near 505, 527, and 576 nm is among the most readily identified patterns in practical gemmology and is clearly resolved on Eickhorst instruments.
• Zircon: The closely spaced absorption lines of zircon — particularly the strong line near 653.5 nm — are a reliable species indicator visible in the spectroscope.

Limitations

The hand spectroscope, including the Eickhorst range, cannot replace quantitative spectrometry for precise wavelength measurement or for detecting subtle spectral shifts associated with geographic origin determination. Very pale or heavily included stones may transmit insufficient light for clear spectrum observation. The instrument is also less effective in reflected-light mode for opaque or heavily saturated materials. For definitive origin reports or treatment detection at the trace level, laboratory-grade ultraviolet-visible spectrophotometry, laser-ablation inductively coupled plasma mass spectrometry, or Raman spectroscopy are required. The hand spectroscope is best understood as a rapid screening and confirmation tool rather than a stand-alone proof of identity.

Place in the Gemmological Toolkit

Alongside the refractometer, polariscope, and Chelsea colour filter, the spectroscope occupies a foundational position in classical gemmological method. The Eickhorst instrument, by virtue of its optical quality and durability, has become a preferred choice in European training programmes — including those affiliated with the Deutsche Gemmologische Gesellschaft (DGemG) — and is commonly encountered on the benches of independent valuers, auction-house specialists, and laboratory gemmologists. Its continued relevance in an era of advanced analytical instrumentation reflects the enduring value of rapid, non-destructive, visually intuitive gemstone examination.