Pleochroism
Explanation and its effects on gemstone color
Delving into the captivating world of gemstones brings to light some remarkable phenomena that contribute to their mystique and beauty. One such fascinating optical characteristic is “pleochroism,” a feature that can significantly influence the color and overall appearance of gemstones. Understanding pleochroism is essential for both gem enthusiasts and professionals alike, as it not only affects the gem’s visual appeal but also its valuation and the approach to gemstone cutting.
Explanation
Pleochroism is derived from the Greek words ‘pleion’ (more) and ‘chroa’ (color) and refers to the optical phenomenon where a gemstone appears to have different colors when observed at different angles, specifically along different crystallographic axes. This occurs because the gemstone absorbs different wavelengths (or colors) of light depending on the direction from which light enters the stone, relating to its internal crystal structure.
In simpler terms, certain light paths within the crystal are color-selective, absorbing some wavelengths of light while transmitting others. Therefore, when you rotate a pleochroic gemstone, you are viewing it along different light paths, each of which may present a distinct color.
The degree of pleochroism can vary among gemstones, with some exhibiting noticeable differences and others having subtle variations that are barely perceptible. Pleochroism is typically categorized into two main types: dichroism, where a gem shows two colors, and trichroism, where it shows three.
Its Effects on Gemstone Color
The pleochroism effect has profound implications for a gemstone’s appearance, especially its color presentation. For gemstones with pronounced pleochroism, the color you perceive can significantly change with the angle of observation. This characteristic can make a single gem appear to be multiple colors, adding to its allure and uniqueness.
However, pleochroism also poses a challenge for gem cutters. The cutting orientation chosen for a pleochroic gemstone can dramatically affect its finished color. Cutters must understand the crystal’s pleochroic nature to showcase the most desirable color or the most intriguing color combination throughout the finished gemstone. A skilled cutter, for instance, may choose an orientation that emphasizes a sapphire’s deepest blue rather than an unwanted greenish tone.
Additionally, pleochroism can influence the value of a gemstone. Stones displaying particularly captivating color changes due to pleochroism can be more desirable to collectors and enthusiasts, thereby commanding higher prices. Conversely, if the pleochroism effect results in unattractive color variations, it might decrease the gemstone’s value.
Pleochroism is a compelling feature of many gemstones, contributing to their enchantment and distinction. This phenomenon underscores the intricate interplay between a gem’s internal structure and the light that dances within it, reminding us that the beauty of these natural art forms is born from their remarkable physical properties and the skill with which they are brought into the light.
Observation Techniques Using a Dichroscope
A dichroscope is a handheld tool that gemologists use to detect and observe the pleochroic colors in gemstones. The device works by presenting two separate images of the stone, side by side, each showing the colors transmitted along the different optical paths within the crystal. Here’s how to use a dichroscope to observe pleochroism:
- Preparation: Begin with a well-lit area, preferably using a single light source. Natural daylight is often the best choice. Ensure the gemstone is clean and free from any smudges or dust that might interfere with your observation.
- Positioning the Gemstone: Hold the gemstone between your fingers or place it in a gem holder. It should be directly under the light source. If possible, use tweezers or a holder to avoid finger reflections interfering with what you see through the dichroscope.
- Using the Dichroscope: Hold the dichroscope in one hand and bring it close to one eye, like a monocular. Position the stone so you can view it through the dichroscope. Look through the viewing window and adjust your position until you can see the gem clearly.
- Observing Pleochroism: As you look through the dichroscope, you’ll see two images of the same area of the stone. These images are the result of the calcite crystal within the dichroscope splitting the light. If the gem exhibits pleochroism, you’ll observe two different colors side by side. These colors represent the different wavelengths absorbed or transmitted along the distinct optical paths in the gemstone.
- Rotating the Stone: While keeping your eye on the images, carefully rotate the gemstone. Pleochroic colors will change or disappear at different angles if the gemstone is pleochroic. Take note of any color changes and the angles at which they occur.
- Documenting Observations: For professional assessments, it’s crucial to document the colors observed at each angle. This information is invaluable for identification, valuation, and further gemological analyses.
- Repeat for Verification: To ensure accuracy, repeat the process several times. Consistent results across multiple observations confirm the presence and degree of pleochroism.
Understanding and correctly implementing these techniques with a dichroscope will reveal the hidden nuances of gemstones, offering insights into their true nature. For anyone passionate about the inner world of gemstones, mastering the use of the dichroscope to explore pleochroism is a skill that amplifies the appreciation of these earthly treasures’ complexity and beauty.