geo4 - Madison 6:17 PM Lecture 4 Color in Gemstones I What...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
2/5/09 6:17 PM :. Madison .: Page 1 of 14 Lecture 4: Color in Gemstones I. What is Color For some gems, color is the most important factor in determining value. Certain gemstones have nearly immutable color, while others vary so endlessly the reasons behind their coloration remain a mystery. To understand the phenomenon of color, one must be familiar with the concept of light. Since this is an intermediate level course, I expect you to understand both the wave and particle behaviors of light. Without this knowledge, any further discussion of color is difficult at best. Visible light is only a small part of the electromagnetic spectrum. Radio waves, light waves, and cosmic rays make up a continuous spectrum of energy. Radio waves have wavelengths up to a billion times longer than visible light, while Cosmic rays have wavelengths a billion times shorter than visible light. Visible light occupies approximately the middle of the spectrum from 400 to 700 nanometers ( billionths of a meter - nm ) . Each color has its own range of wavelengths. Red light occupies 630 - 700 nm, while Violet light has wavelengths of 400 - 430 nm. If you've ever seen a rainbow, you've seen the seven basic colors of light: Red, Orange, Yellow, Green, Blue, Indigo, and Violet. Electromagnetic Radiation is a continuous spectrum of energy from long-wavelength radio waves to very, very short-wavelength cosmic rays. Note that this is not to scale. Our perception of color occurs when specific of wavelengths of light strike certain cells on the back of our eyes. For instance, if light of 700nm wavelength were to hit our eyes, we would perceive it as red light, just as we would perceive 400nm wavelengths to be violet. You should also note that light from several wavelengths together form other colors. All wavelengths together ( as you should already be aware ) form white light, while no light is black. Note, however, that this is not quite the same principle as additive mixing in paint
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2/5/09 6:17 PM :. Madison .: Page 2 of 14 pigments. If an object absorbs most wavelengths of light and reflects only specific ones back to our eyes, the object will appear to be that color. Thus if a gem reflects light of 700 - 630 nm, it will appear red ( and so on ) . Herein lies the most important concept behind color in gemstones. Gems are different colors because they reflect specific wavelengths of light. Here the violet colored gemstone is reflecting violet light wavelengths, while absorbing all the others. You should also remember my comment from last week: a blue sapphire will appear black in
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/11/2009 for the course GEO 331 taught by Professor Huifang during the Spring '07 term at University of Wisconsin.

Page1 / 14

geo4 - Madison 6:17 PM Lecture 4 Color in Gemstones I What...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online