Gem_5109 Uses of Non Visible Energy in Gemology
- Energy and Non Visible Radiation
- Luminescence (Fluorescence and Phosphorescence)
- Construction, uses and Typically results of ultra violet lamp.
- The uses of X-ray in gemology
- Thermal Conductivity and Electrical Conductance probes
- Reflectance Meters
1.1 Energy and Nonvisible Radiation
Introduction to Nonvisible Energy:
Electromagnetic Spectrum Overview: The electromagnetic spectrum encompasses all types of electromagnetic radiation, ranging from high frequency gamma rays to low frequency radio waves. Visible light occupies only a small portion of this spectrum, approximately from 380 nm to 750 nm.
Nonvisible Radiation Types: These include ultraviolet (UV) radiation, X-rays, infrared (IR) radiation, microwaves, and radio waves, each with distinct properties and uses.
Types of Nonvisible Radiation:
Ultraviolet (UV) Light:
UVA (315400 nm): Least harmful, can cause tanning.
UVB (280315 nm): Can cause sunburn, more harmful to living tissues.
UVC (100280 nm): Most harmful, absorbed by the Earth’s atmosphere.
X-rays: Have wavelengths ranging from 0.01 to 10 nm and can penetrate most materials, making them useful for imaging internal structures.
Infrared (IR) Radiation: Wavelengths range from 700 nm to 1 mm, experienced as heat, and used in thermal imaging and spectroscopy.
Applications in Gemology:
Gem Identification: Different gemstones absorb and emit nonvisible radiation in unique ways, aiding in their identification.
Detecting Treatments and Enhancements: Nonvisible radiation can reveal treatments such as dyeing, coating, or irradiation that may not be apparent in visible light.
Quality Assessment: Helps in assessing the internal structure, inclusions, and overall quality of gemstones.
1.2 Luminescence (Fluorescence and Phosphorescence)
Definition and Mechanism:
Luminescence: Emission of light by a material when it absorbs photons. Unlike incandescence, luminescence does not result from heat.
Mechanisms of Luminescence:
Fluorescence: Immediate emission of light upon exposure to UV light. Ceases almost instantly when the light source is removed.
Phosphorescence: Similar to fluorescence but the emitted light continues for some time after the light source is removed due to delayed reemission of absorbed energy.
Fluorescence:
Characteristics: Common in diamonds, some rubies, and sapphires. Fluorescence can vary in color, intensity, and pattern.
Applications: Used in verifying gemstone authenticity and detecting treatments.
Phosphorescence:
Characteristics: Observed in some varieties of fluorite and certain diamonds known as “chameleon diamonds.”
Applications: Helps in identifying specific types of gemstones and their origins.
Importance in Gemology:
Identification: Fluorescence and phosphorescence provide diagnostic properties that can distinguish between natural and synthetic gemstones or identify specific treatments.
Aesthetic Appeal: In some cases, the presence of luminescence can enhance the gemstone’s value and appeal.
1.3 Construction, Uses, and Typical Results of Ultraviolet Lamp
Construction:
Components:
UV Bulb: Emits UV light in specific bands.
Housing Unit: Contains and protects the bulb, often with filters to select the desired UV wavelength.
Filters: Used to block visible light and allow only UV light to pass.
Types:
Handheld Lamps: Portable and convenient for fieldwork.
Stationary Lamps: Larger, more precise, used in laboratory settings.
Uses in Gemology:
Identification: Different gemstones fluoresce uniquely under UV light, aiding in their identification.
Natural Diamonds: Typically show blue fluorescence under UVA light.
Synthetic Diamonds: May show different patterns or colors of fluorescence.
Detection of Treatments: UV light can reveal surface treatments such as coatings or dyes.
Quality Assessment: The fluorescence of diamonds can affect their grading and market value.
Typical Results:
Blue Fluorescence: Common in diamonds, with intensity ranging from faint to strong.
No Reaction: Some gemstones, like emeralds, may show no fluorescence.
Distinct Patterns: Synthetic or treated gems may exhibit unique fluorescence patterns distinct from natural stones.
1.4 The Uses of X-ray in Gemology
Introduction:
Nature of X-rays: High-energy electromagnetic radiation with wavelengths shorter than UV light, capable of penetrating most materials.
Applications: X-rays are invaluable for nondestructive testing and internal examination of gemstones.
Applications:
Identifying Inclusions:
Internal Flaws: X-rays can reveal inclusions and internal structures not visible to the naked eye.
Gemstone Clarity: Helps in assessing the clarity grade of gemstones.
Detecting Synthetic Gems:
Growth Patterns: Synthetic gems often have distinct internal growth patterns that differ from natural stones.
Inclusion Types: Specific types of inclusions can indicate synthetic origin.
Quality Control:
Authenticity Verification: Ensures the gemstone is natural and untreated.
Treatment Detection: X-rays can reveal treatments such as fracture filling.
Types of X-ray Techniques:
X-ray Diffraction (XRD):
Principle: Measures the diffraction of X-rays through a crystal structure.
Application: Determines the crystalline structure and can identify mineral species.
X-ray Fluorescence (XRF):
Principle: Measures secondary X-rays emitted by a material when it is excited by a primary Xray source.
Application: Determines the elemental composition of a gemstone, useful for identifying and verifying gemstones.
1.5 Thermal Conductivity and Electrical Conductance Probes
Thermal Conductivity Probes:
Function:
Measurement: Measures the rate at which heat is conducted through a gemstone.
Principle: Different materials conduct heat at different rates. Diamonds, for instance, have very high thermal conductivity.
Uses:
Diamond Testing: Quickly distinguishes diamonds from simulants like cubic zirconia.
Gemstone Identification: Useful for identifying gemstones with high thermal conductivity.
Electrical Conductance Probes:
Function:
Measurement: Measures the electrical conductivity of gemstones.
Principle: Gemstones like moissanite have electrical properties that differ from diamonds.
Uses:
Moissanite Detection: Identifies moissanite, which is electrically conductive, unlike diamonds.
Gemstone Verification: Confirms the identity of gemstones based on their electrical properties.
Construction:
Sensor: Contacts the gemstone and measures its thermal or electrical properties.
Display Unit: Provides a readout of the measurements, often digitally.
Handheld Devices: Portable and convenient for quick field testing.
Applications in Gemology:
Nondestructive Testing: Provides reliable results without damaging the gemstone.
Rapid Identification: Allows quick differentiation between gemstones and their simulants.
1.6 Reflectance Meters
Introduction:
Reflectance: The amount of light reflected off the surface of a gemstone. It provides information about the surface polish and luster.
Importance: Reflectance measurements help in assessing the quality and authenticity of gemstones.
Construction:
Components:
Light Source: Illuminates the gemstone.
Detector: Measures the reflected light.
Digital Display: Shows the reflectance value.
Types:
Handheld Reflectance Meters: Portable for field use.
Laboratory Reflectance Meters: More precise and used for detailed analysis.
Uses in Gemology:
Surface Analysis:
Polish Quality: High reflectance indicates a well polished gemstone.
Surface Condition: Helps in identifying surface scratches or imperfections.
Gem Identification:
Material Properties: Different gemstones have characteristic reflectance properties based on their surface and internal structure.
Luster Assessment: Determines the type and quality of luster (e.g., vitreous, silky, metallic).
Typical Results:
High Reflectance:
Indicates: Well polished, high-quality gemstones.
Examples: Diamonds, sapphires, and rubies.
Low Reflectance:
Indicates: Surface roughness, lesser quality polish, or different material properties.
Examples: Rough or unpolished gemstones, less dense materials.