How light and light affect the color of gemstones

As you have discovered, gemstones may look a little different in color under different light, and even look very, very different at different times of the day, morning, noon, and afternoon. This article describes the interaction between color, light, and gemstones, and how we can explain this phenomenon.

In colored gemstones, color is king. Color is the most valuable factor in 4C, and it is obvious that this is an important part of evaluating the quality of gemstones.
Observing the light of gemstones will have a great impact on our eyes' interpretation of color. If we are to decipher the reasons, we need to understand some basic knowledge behind the spectrum and the actual cause of people's perception

The reason for the color. When you understand this, the problem that many gems have different colors under different light can be solved.

What the hell is light?

First of all, what is light? Light is part of the wavelength spectrum of electromagnetic waves. These specific wavelengths, when they enter the human eye, are interpreted as colors. According to the observed wavelength, light is perceived as a variety of colors, and the light we can see is only a small part of the huge spectrum of electromagnetic energy. This large spectrum also includes visible radiation, such as radio waves, WeChat, and X-rays.

The prism shows the diffusion of white light into the visible spectrum. We see light from the sun or ordinary light bulbs, which is produced by mixing the entire range of visible light. When a beam of light passes through the edge, it will spread out in a certain order according to various waves. The resulting light band, the shortest light wave at one end produces a purple feeling, followed by longer waves, and the blue, green, yellow, orange and red areas we feel are exactly the same as when we watch the rainbow.

White light sources have different energy distributions in different color and wavelength regions in the visible spectrum. So we feel warmer and yellower white light from standard incandescent bulbs. In many fluorescent tubes, we feel colder and bluer white light. This is because incandescent bulbs emit more light in long waves than in short waves, so they emit yellow light. Fluorescence tubes emit weaker light in long waves and intense light in green and blue.

In contrast, the sun also has its own version of white light, because its radiation is distributed around the blue-green broad peak, and the sides are gradually tapering.

Here we talk about what light is. I believe everyone has a certain understanding. The spectrum is a huge energy spectrum. The white light we see is composed of different light waves. From red-orange-yellow-green-cyan-blue-purple, from long wave to short wave. Why some look yellow and warm is because the long wave is longer, and why some look cold is because the short wave is longer. Although they eventually form white light, because the long wave and short wave segments are different, the hue and feeling of reproduction are also different. Here, let's make the light clear first.

What is color?

Let's have a classic question. If a pair fell on the other side of the earth, but no one heard it, would it make a sound? This question applies to color. If a blue sapphire is placed in a safe, does it have color? This is a controversial topic.

In reality, we are used to using color as an attribute of an object, such as shape or size, but unlike atomic matter that can ultimately increase the weight or mass of an object, color is not objective and independent. It is an explanation of our own feelings and exists as the perception of the viewer, not the atom of the object.

The colors come from our sensory devices, our eyes and our brains.

Drawing the point, when we are describing the colors of gemstones, we are actually describing the feelings produced by a complex physiological process.

The color we see is actually reflected back to our eyes by what we call visible light wavelengths, and the color of other wavelengths is absorbed. Therefore, the luster color of the gem does not emanate from the inside of the gem.

Color comes from light and the interaction of light energy with trace elements inside the gemstone, just like light is split by a prism, and different wavelengths are regarded as different colors.

Therefore, we consider this point according to the context. For example, the shafflite appears green in light, indicating that the shafflite absorbs more visible wavelength waves than short wavelength waves. When sunlight hits the shafflite, it will return to our eyes. Unabsorbed light is higher in short waves (green and blue) and weaker in long waves (red, orange, yellow).

So when these light waves are attracted, our vision will process the shorter waves into a green feeling.

For rubies, the situation is just the opposite, such as rubies. It absorbs most of the short light waves, while for long-wave visible light, when sunlight hits the ruby, it returns to the eyes, giving us a sense of ruby. On the other hand, if the same ruby is placed in green light (green light filtered in the spectrum), the ruby tends to absorb shorter wavelengths, and the lack of long waves in the light source causes the ruby to appear more gray.

Gemology and Spectroscopy

Among the optical tools gemologists use to identify different types of gemstones is a spectroscope. This tool allows gemologists to determine the spectrum of the gemstone. Shows which lengths are absorbed. This is a very good identification test. It can be explained according to the above example. Below is the spectrum of ruby and shafflite. The black lines in it show which colors are absorbed.

The spectrum seen through the spectroscope, on the left is the ruby spectrum that absorbs most of the short waves and appears red. On the right is the spectrum of Shaffley.

Light and Gem Summary

Light produces color, and different gemstone minerals absorb different wavelengths of light, causing our eyes to perceive different colors of objects accordingly. This is why rubies appear incomparably red under incandescent light, and very inconspicuous under shorter wavelengths of green light. This is also why tanzanite appears very much under fluorescent light, and more purple under incandescent light.

Even at different times of the day, the quality of the light changes over time, and the gemstone changes its color.

From a scientific point of view, the light used to grade gems is an important reference factor. Maintain consistency. But in terms of sensibility, when we choose gems, we should follow our own standards. We can choose whatever color we like.