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UV lamp is an important auxiliary identification instrument. It is mainly used to observe the luminescence of gemstones. The fluorescence characteristics of gemstones under long and short wave ultraviolet light can help identify gemstones.

Working principle

UV lamp tubes emit ultraviolet light waves within a certain wavelength range. After passing through a specially designed filter, only ultraviolet light with a main wavelength of 365nm or 253.7nm is emitted. When different wavelengths of ultraviolet light shine on gemstones, they emit fluorescence of different colors and brightness. This helps identify gemstones based on their fluorescence characteristics.

Types and characteristics of gemstone ultraviolet lamps

The ultraviolet lamps used for jewelry identification are mainly divided into two categories: dark box ultraviolet fluorescent lamps (Figure 1) and ultraviolet fluorescent flashlights (Figure 2).

Figure 1: Dark box ultraviolet fluorescent lamps

Figure 2: Ultraviolet fluorescent flashlights

Operation steps

1. Clean the gemstones, place them in the dark box, and then close the dark box.
2. Turn on the switch, press the long wave (LW) or short wave (SW) buttons respectively, and observe the luminescence of the gemstone with your eyes close to the fluorescent lamp eyepiece.
3. Record the observed luminescence phenomenon of gemstones.
4. Turn off the UV light and continue to observe. If the gemstone still emits light, it indicates phosphorescence and should be recorded.
5. Take out the gemstone and turn off the UV fluorescent lamp.

Precautions

1. UV light is harmful to the eyes. Do not look directly at the UV lamp. Place the sample first before turning on the switch.
2. Use tweezers to handle gemstones to prevent UV light damage to skin.
3. Pay attention to fluorescence of dyed and filled gemstones.
4. Reflection of light on the surface can be mistaken for fluorescence.
5. Fluorescence may differ significantly between samples of similar gemstones.
6. Fluorescence of transparent samples differs from opaque samples.
7. UV light is only an auxiliary method and should be used with other identification techniques.

Main uses

Assist in identifying gemstone varieties:
Different gemstones have different fluorescence characteristics, which can distinguish them. For example, ruby versus red garnet: ruby has red fluorescence, while red garnet shows no fluorescence. Sapphire versus Benitoite: blue sapphire often lacks fluorescence under shortwave ultraviolet light, while Benitoite shows strong blue-white fluorescence.

Help distinguish diamonds and diamond imitations:
Diamond fluorescence under ultraviolet light varies from none to strong, with various colors visible (Figure 3). Most imitations exhibit only a single fluorescence color, making UV light useful for identifying group-set diamonds and loose diamonds.

Figure 3: Fluorescence performance of various diamonds

Help distinguish synthetic and natural gemstones:
Natural sapphires generally do not fluoresce under short wave UV light, while synthetic sapphires show a unique milky white fluorescence. Most synthetic emeralds emit bright red fluorescence under long wave UV light, which is significantly different from natural emeralds.

Help identify manually optimized gemstones:
Natural jadeite generally has no or weak fluorescence under UV light, while some “B-grade” jadeite that has been bleached and filled shows obvious fluorescence (Figure 4).

Figure 4: Comparison of natural light and ultraviolet fluorescence of different jadeite