A single polished stone sitting on a jeweller's counter can represent thousands of dollars, or it can be worth almost nothing. The difference comes down to one question: is it real? Consumers, collectors, and even some retail buyers fall for synthetic and imitation stones every year because they rely on appearance alone. Appearance, unfortunately, is the easiest thing to fake.
At GTCL, our gemologists apply five core tests before issuing a certificate. Each test targets a different physical property that imitations struggle to replicate.
1. Visual Inspection Under 10x Magnification
Natural gemstones almost always contain inclusions: tiny crystals, silk-like rutile needles, gas bubbles, or growth lines. A stone that appears perfectly clean under 10x magnification is more likely to be synthetic or glass. Gemologists look for inclusion patterns characteristic of each stone type. A natural ruby, for instance, will show silk-like rutile needles, while a flame-fusion synthetic ruby appears nearly flawless with curved growth lines.
2. Refractive Index Measurement
Every mineral bends light at a measurable angle. A refractometer reads this angle to two decimal places. Natural sapphire consistently shows an RI between 1.762 and 1.770. Glass, which is commonly used to imitate coloured gems, falls in the 1.50 to 1.52 range. This one reading eliminates a large percentage of fakes immediately.
3. Specific Gravity Test
Specific gravity (SG) measures how dense a stone is relative to water. The test uses hydrostatic weighing: the stone is weighed in air and then in water, and the ratio reveals its density. A genuine diamond (SG 3.52) is noticeably heavier than cubic zirconia (SG 5.65 to 5.95), which actually feels too heavy for its size. Each gem species has a documented SG range, and falling outside that range is a red flag.
4. Spectroscopic Analysis
A gemstone's colour comes from specific trace elements absorbing certain wavelengths of light. A spectroscope breaks white light into its component wavelengths and shows which ones the stone absorbs. A natural emerald coloured by chromium will show distinct absorption bands in the red and violet portions of the spectrum. A green glass imitation will show a completely different, usually featureless, spectrum.
5. Fluorescence Under UV Light
Exposing a stone to long-wave and short-wave ultraviolet light can reveal telltale reactions. Natural diamonds frequently fluoresce blue under long-wave UV, while certain synthetics glow differently. Burmese rubies often show a strong red fluorescence under both long-wave and short-wave UV, a reaction that helps separate them from garnets and red spinels that look similar to the naked eye.
Why Lab Certification Matters
These five tests form the foundation of gemological identification, but they work best in combination. A single test can be inconclusive. A trained gemologist at an accredited lab weighs all the evidence together, then issues a report that records every measurement and observation. This report becomes the stone's permanent identity document.
Before buying any gemstone of significant value, request a lab certificate from a recognized testing laboratory. The certificate protects your investment and gives you an independent, scientific verification of what you own.
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