Lab Equipment
Reference tools for gemological lab equipment including Chelsea filter reactions, spectroscope absorption lines, and heavy liquid separation.
Chelsea Filter
Expected colour reactions for gem identification
The Chelsea filter transmits deep red and yellow-green light, filtering out other wavelengths. Chromium-bearing gems fluoresce red.
Emerald (Natural Colombian)
Chrome-coloured emeralds fluoresce
Emerald (Natural Zambian)
Iron-rich, less chromium
Emerald (Synthetic)
Often brighter than natural
Ruby (Natural)
Chromium fluorescence
Sapphire (Blue)
No chromium, no reaction
Synthetic Blue Spinel
Cobalt-coloured shows red
Synthetic Green Glass
Chromium in glass
Alexandrite
Strong chromium content
Jadeite (Natural)
Dyed jadeite may show pink
Peridot
Iron-coloured, no reaction
Diamond
No reaction expected
Important Limitations
- • Not definitive: Chelsea filter alone cannot prove natural vs synthetic
- • Origin matters: Different emerald sources react differently
- • Lighting critical: Use strong light source for best results
- • Combine tests: Always use with other identification methods
How It Works
The Chelsea filter is a didymium glass filter that transmits deep red (around 690nm) and yellow-green (around 570nm) light. Gems containing chromium fluoresce under the filter, appearing red or pink. This is especially useful for screening emeralds and detecting some synthetic stones.
Spectroscope Calculator
Wavelength ↔ colour converter and absorption line reference
Enter a wavelength (380-780nm) to see its colour, or browse common absorption lines by gem.
Common Absorption Lines (15)
Ruby
StrongChromium doublet at 694.2 and 692.9nm
Ruby
MediumBroad band
Ruby
MediumFine line
Emerald
WeakChromium line
Emerald
WeakChromium doublet
Alexandrite
StrongChromium doublet
Jadeite (Green)
MediumChromium (dyed may show)
Demantoid Garnet
StrongCharacteristic horsetail band
Zircon
StrongUranium lines
Diamond (Yellow)
MediumCape series
Peridot
StrongIron triplet
Peridot
StrongCentral line of triplet
Peridot
StrongIron triplet
Sapphire (Blue)
MediumIron-titanium
Aquamarine
WeakIron absorption
Spectroscope Usage
- • Use a strong white light source for best results
- • Absorption lines appear as dark bands against bright spectrum
- • Some gems show many lines, others show few or none
- • Position matters - some lines only visible in certain orientations
Spectroscope Band Matcher
Tick observed absorption bands to rank candidate species
Tick every absorption line you can see in the spectroscope. The reasoner ranks species whose stored band patterns match. Selective (diagnostic) bands are weighted more heavily.
Observed bands
UV Fluorescence Lookup
Match observed long-wave / short-wave UV reactions to gem species
Observe the stone under both long-wave (365 nm) and short-wave (254 nm) UV in a darkened cabinet and report what you see. The reasoner ranks species whose stored fluorescence text matches your observation.
Long-wave (365 nm)
Short-wave (254 nm)
Heavy Liquid Reference
SG separation guide by liquid density
Heavy liquids separate gems by specific gravity. Select a liquid to see which gems float or sink.
Heavy Liquids
Gem SG Reference
⚠️ Safety Warning
- • Heavy liquids are highly toxic - avoid skin contact and fumes
- • Always use gloves, safety glasses, and work in a fume hood
- • Store in sealed containers away from light (causes decomposition)
- • Never use with porous or fractured stones - liquid can be absorbed
- • Dispose of according to hazardous waste regulations
Alternative: Hydrostatic Weighing
For most gem identification, hydrostatic weighing (measuring weight in air vs water) is safer and more accurate than heavy liquids. Heavy liquids are mainly used for quick separation of parcels or when hydrostatic equipment isn't available.