Light Behavior in Gemstones
Expanding on the behavior of light in gemstones, we encounter the factors of beauty.
Refraction is the change of direction & speed of light when entering a gemstone. Refraction is one of the components that creates the effects that results in the beauty of gemstones.
Reflection is the "bounce" of light after it strikes a surface. The angles of incidence and reflection are equal.
The observed quantity of light reflected is partly a factor of the quality of the surface. And the harder a gem, the better the quality of the surface than can be created.
Reflection can be external or internal. Internal reflections in transparent gemstones is how light returns to the eye.
Reflections off inclusions in semi-transparent or opaque gems can create a variety of light and color effects such as aventurism.
Iridescence is a form of interference that usually involves the refraction and reflection in thin films or layers of gas or liquid. The result is the "rainbow effect".
Interference is an important effect that is often difficult to grasp. Basically, the effect is produced when two or more waves of light are traveling on the same path after having traveled different distances.
Their "phase" relationship is important to the concept. Waves in phase with each other reinforce the color. Waves exactly out of phase with each other will cancel each other. In effect, they interfere with each other.
An infinite number of phase possibilities exist. What we observe are those light rays left over after reinforcement and cancellation.
White light is a mixed of all colors of the spectrum. When subjected to the phenomena of interference, white light will be perceived as light that is missing certain colors. This is the result of the cancellation of certain waves.
Other colors will have been reinforced and be perceived as more vivid. The play of color in opal is a good example of an interference effect on light.