Gemstone Windows and Dark Patches: What to Look for in a Cut Gem

-
Image
AI-generated educational illustration. Conceptual only; not a photograph of an actual specimen or location. A coloured gem may have a pale, see-through centre or areas that look almost black. Both affect its appearance, but they do not have the same cause. What is a window? A window is an area where light passes through the gem instead of being returned towards the viewer. You may see the background through it, especially near the centre. Cutting angles and the material's refractive index—how it bends light—help determine whether this happens. There is no single ideal depth for every gemstone. Why dark patches need a closer look Darkness can have several causes. The material may absorb a lot of light. Some facets may reflect dark surroundings or the observer. Extinction is another cause, involving light that is not returned to the viewer after internal reflection. For that reason, calling every black patch “extinction” can be misleading. A simple viewing routine Look at the gem fac...
Post a Comment

Gemological Refractometer

-

 

Refractometer

Construction of Refractometer

A refractometer consists of a light source, a contact liquid chamber, and an optical system for measuring the refractive index of a substance.

Sources of Illumination (Sodium Light)

Sodium light is commonly used as a source of illumination in refractometers due to its monochromatic nature.

Contact Liquid

The contact liquid is used to ensure proper contact between the substance being measured and the refractometer prism. It helps minimize air gaps and improves the accuracy of the measurement.

Using the Refractometer

To use the refractometer, follow these steps:

  1. Place a few drops of the contact liquid on the prism.
  2. Open the cover plate and ensure the prism is clean and dry.
  3. Close the cover plate and wait for the temperature of the refractometer to stabilize.
  4. Open the cover plate again and place a drop of the substance being measured on the prism.
  5. Close the cover plate and look through the eyepiece.

Taking Reading

To take a reading, observe the boundary between the illuminated and dark areas in the field of view. The refractive index can be read directly from the scale.

Use of the Polarizing Filter

A polarizing filter can be used in some refractometers to enhance the visibility of the boundary between the illuminated and dark areas. It helps reduce glare and improves accuracy.

Optical Character (SR/DR)

The optical character of a substance can be determined using a refractometer. It can be categorized as either singly refracting (SR) or doubly refracting (DR) based on its behavior when interacting with light.

Uniaxial

A uniaxial substance exhibits a single optical axis and behaves differently in different crystallographic directions.

Biaxial

A biaxial substance exhibits two optical axes and behaves differently in different crystallographic directions.

Birefringence

Birefringence refers to the property of a substance to split a light beam into two polarized rays with different refractive indices. It is often observed in biaxial substances.


Comments

Post a Comment

Post a Comment Please. we love hearing from you.

Popular posts from this blog

Introduction quiz

-
💎 Gemology Quiz 1. What does gemology study? The study of rocks only The study of gemstones and their properties The study of fossils 2. Who is a gemologist? A person who mines gemstones A person who designs jewelry A person who identifies gemstones using instruments 3. Which of the following is NOT a characteristic of a mineral? Naturally occurring Organic in nature Has a defined chemical composition 4. What makes a gemstone valuable? Only its size Beauty, rarity, and durability Color only 5. Which of the following is an organic gem? Sapphire Pearl Emerald 6. The Mohs scale measures what property? Toughness Hardness Transparency Submit Quiz Further reading introduction to gemology Gemology MCQs Part-1
Read the full guide

Gemology MCQ Quiz Part 6: Test Your Gemstone Knowledge

-
Image
Gemstone MCQs Quiz Test Your Knowledge in Gemology Part 6 1. A 2-carat fine-quality ruby is worth more than 10 rubies of the same color and quality, which have a total weight of 4 carats . a) True b) False Correct Answer: a) True 2. One carat equals: a) 1 gram b) 1/10 of a gram c) 1/5 of a gram d) 1/2 of a gram Correct Answer: c) 1/5 of a gram 3. A ten-pointer is a stone that weighs: a) 10 carats b) 1/10 of a carat c) 10 facet junctions d) 10 grams Correct Answer: b) 1/10 of a carat 4. When comparing gem prices, you should compare their: a) Per-carat cost b) Overall size c) Density d) Facet count ...
Read the full guide

Gemology MCQs Part-3

-
Image
Gemology MCQs Gemology Multiple-Choice Questions 21. Separating natural pink sapphire from synthetic pink sapphire commonly relies upon a microscopic study. True False 22. In a round brilliant cut, the total number of facets is: 57 59 60 None of the above 23. A spectroscope is used to detect the spectrum. True False 24. Refraction is the bending of light. True False ...
Read the full guide