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

Coral Gem Identification: Natural Colour, Dye and Imitations

-

A red bead is not automatically natural-colour precious coral. Gem coral includes different animal skeleton materials, and the market also contains dyed products and imitations. Understanding the material and understanding its colour are two separate parts of identification.

Different corals have different structures

SSEF’s 2005 overview distinguishes calcitic precious coral, aragonitic blue coral and corals with horn-like organic skeletons. Their structures and physical properties differ. Fossilised coral may also have undergone mineral replacement, so it should not be treated as identical to recent coral.

Clues to dye and resin

Dye may collect in pores, fissures or other open spaces. Resin may appear as a different substance within these areas. Drill holes can sometimes expose useful clues that are hidden on a polished outer surface.

These observations are clues, not a complete home test. A clean-looking surface does not prove natural colour. SSEF describes combining microscopy with Raman spectroscopy to investigate the material and its colouring substances.

How shell can imitate coral

Dyed shell beads can resemble coral. Mineral identification helps distinguish aragonitic shell from calcitic precious coral, while layered structures can provide supporting evidence. Ask for the actual material name and a clear treatment description. A label such as red coral may leave both questions unanswered.

Sources and further reading

SSEF Swiss Gemmological Institute, Facette, issue 12, January 2005, pp. 6-7, “Coral en Vogue: Revival due to fashion trends”. Read the original SSEF PDF.

This independent educational article explains historical SSEF research in original, simple English. It is not an SSEF publication. No source photographs or illustrations are reproduced.

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