Chapter 7 Key Concepts & Terms Flashcards
What is the relationship between the angle of incidence and the angle of reflection?
They are always equal.
What is the refractive index (RI) of air assumed to be in gemology?
1.
Do all gem materials have RIs higher than 1?
Yes.
How does light travel in materials with higher optical density compared to lower optical density?
Light travels more slowly.
When does refracted light bend toward the normal?
When traveling from a less refractive material to a more refractive material.
When does refracted light bend away from the normal?
When traveling from a more refractive material to a less refractive material.
What is the relationship between refractive index and critical angle?
Higher RIs have smaller critical angles.
What is the critical angle of diamond?
24.5 degrees.
How does diamond’s small critical angle affect light?
It limits the opportunity for light to exit the stone.
What does dispersion measure in a material?
The RI difference between the violet and red light rays.
Is dispersion an optical property that varies by material?
Yes.
What happens to light absorption as it travels further in a gemstone?
More absorption occurs.
What is diamond’s brightness related to?
The amount of light reflected back to the observer.
What does a diamond’s face-up pattern reveal?
Nearly all of the cutter’s fashioning choices.
What term do diamond professionals use to describe a diamond’s display of dispersion?
Fire.
What is the best way to see a diamond’s fire?
Look at the stone face-up while rocking and tilting it.
How does absorption affect the color of colored diamonds?
More absorption causes deeper color; less absorption causes lighter color.
How can cutting alter a diamond’s color appearance?
By changing the length of the path of light in the diamond.
What is the GIA Cut Grading System based on?
Both scientific research and observation.
What does each cut grade in the GIA Cut Grading System include?
A range of proportion combinations and a variety of appearances.
To what diamonds does the GIA Cut Grading System apply?
Round brilliant diamonds in all clarities across the D-to-Z color range.
What is a combined evaluation in the GIA Cut Grading System based on?
Face-up appearance, design, and craftsmanship.
What can affect a diamond’s appearance?
Variations in lighting and surroundings.
What type of lighting helps evaluate a diamond’s brightness?
Diffused fluorescent lighting.
What is Adamantine?
The highest degree of luster possible in a transparent material.
Adamantine is often associated with diamonds and other gemstones that exhibit exceptional brilliance.
Define the angle of incidence.
The angle at which light hits a surface or boundary, measured between the normal and the incident light.
This angle is crucial in understanding how light interacts with different surfaces.
What is the angle of reflection?
The angle at which light returns from a surface or boundary, measured between the normal and the reflected light.
The angle of reflection is equal to the angle of incidence.
Define the angle of refraction.
The angle at which light bends when it travels from one material to another, measured between the refracted light ray and the normal.
This bending occurs due to a change in speed as light enters a different medium.
What does brightness refer to in terms of diamonds?
The effect of all the diamond’s internal and external reflections of white light.
Brightness contributes significantly to the overall visual appeal of a diamond.
What is the critical angle?
The angle of incidence at which the angle of refraction reaches 90 degrees and total internal reflection begins to occur.
This concept is important in understanding how light behaves in gemstones.
Define dispersion.
The optical phenomenon of white light separating into spectral colors.
Dispersion is responsible for the colorful flashes seen in gemstones.
What does luster refer to?
The appearance of a material’s surface in reflected light.
Luster can vary from dull to brilliant, affecting the gemstone’s aesthetic.
What is a normal in optics?
An imaginary line perpendicular to the surface of a boundary.
The normal is used as a reference for measuring angles of incidence and reflection.
Define optical density.
The ability of a medium or material to slow down the light that travels in it.
Higher optical density results in a greater reduction in light speed.
What is path length in terms of light?
The total distance a light ray travels in a gemstone.
Path length affects the intensity and color of light that emerges from the gemstone.
Define pattern in the context of gemstones.
The relative size, arrangement, and contrast of bright and dark areas when viewed face-up.
A well-defined pattern enhances the visual appeal of a gem.
What does polish refer to in gemstones?
The overall condition of the facet surfaces of a finished diamond.
A good polish improves light reflection and overall appearance.
What is reflection in optics?
The light returned when it hits a surface or a boundary between two different materials.
Reflection is key to understanding how light behaves on gemstone surfaces.
Define refraction.
The change in speed and possible change in direction of light as it travels from one material to another.
Refraction is a fundamental principle in optics, impacting how we perceive gemstones.
What is the refractive index?
A measure of the change in speed and direction as light travels from the air to a certain material.
The refractive index is critical in characterizing gemstones.
Define symmetry in gemstones.
The exactness of a finished gem’s shape and facet placement.
High symmetry is often associated with higher quality in gemstones.
What is total internal reflection?
Complete reflection of a light ray within a material.
This phenomenon is essential for the brilliance seen in diamonds.
