Lesson Category: gemmology

Let’s talk about colour-change gems. The Alexandrite Crystal Barrel is the most sought after, but there are many others such as sapphires, garnets, fluorite, diopside, spinel, tourmaline, and even zultanite that exhibit this unique phenomenon. To observe colour change, you need to use different types of lighting including a pen light, white light, and incandescent light. The lesson also delves deeper into the history of the Alexandrite Crystal Barrel and how it got its name. You will also discover how man-made synthetic cubic zirconia can change colour, and how heat can change colours in materials such as plastics.

In this lesson, you will learn all about the fascinating world of Opals. You will discover the different types of phenomenal Opals, including white and black Opals, and how they are formed. You will also learn about the play of colour that is found in Opals and how it creates a stunning display of light and colour. Tanja will take you on a journey through the history of Opals, exploring their origins in Australia and their recent discovery in Ethiopia. You will also learn about the different colours that can be found in Opals, with red being one of the most valuable.

In this lesson, you will learn all about moonstone and its unique billowy light effect, called adularescence. Moonstone is a popular gemstone that is culturally significant in many cultures, including Indian culture, where it is one of the nine stones on a special pendant. When looking for high-quality moonstone, it’s important to look for transparent stones with strong flashes of blue light. However, moonstone is naturally a Type 3 gem, meaning it typically has lots of inclusions, including centipede-like inclusions. While not all moonstones show adularescence, it is a special effect that makes the stone more valuable. The lesson also covers man-made adularescent material made from glass, often marketed as opalite, which can be convincing but can be identified by gas bubbles inside.

In this lesson, learners will discover the fascinating phenomenon of aventurescene or glitter effect found in materials such as aventurine quartz and Sunstone. You will learn how to identify the presence of mica, the mineral responsible for the sparkle and glitter effect, using a penlight to detect it. Discover how man-made aventurescene is produced in glass, which is readily available in various colours, shapes, and sizes. Tanja will also highlight the importance of properly identifying gemstones to avoid making costly misjudgements in the market.

In this lesson, you will learn about the different types of chatoyancy in gemstones, with a focus on cat’s eye crystal barrel. You will discover what to look for in cat’s eye crystal barrel, including the eye and colour, and how to identify it both in natural and man-made forms. You will also learn about other gems that exhibit chatoyancy, such as tigers eye and hawks eye, and how to identify them.

Tanja will also covers seraphinite and charoite, two lesser-known gems that are gaining popularity in the West. Through video demonstrations and examples, you will gain a deeper understanding of chatoyancy and how it adds unique and striking visual appeal to gemstones. Whether you are a gemstone enthusiast or a professional jeweller, this lesson will broaden your knowledge of this fascinating aspect of gemmology.

In this lesson, you will learn about asterism, the star effect found in certain gemstones. Tanja will explain that star rubies, star sapphires, and black star sapphires are some of the most commonly known materials with asterism. She demonstrates how to use a pen light to find the best angle to view the star in these stones, and what to look for when determining their quality.

The lesson also covers other materials that can have asterism, including moonstones, quartz, rose quartz, and garnet. Tanja will explain how asterism occurs due to specific inclusions within certain stones, and how they are cut to exhibit the star effect properly. She will also touch on man-made asterism, specifically the Lindy Star Sapphire, and how to tell if a stone is synthetic or natural.

Welcome to the next Gemmology chapter about Pearls. Explore their captivating history, types, and value factors. Discover the association of pearls with royalty, and learn about various kinds, such as Akoya, South Sea, Freshwater, Mabe, Keshi, Conch, and Melo Melo. Understand the value factors influencing pearl purchases and appreciate pearls’ roles across different historical periods.

Delve into the formation and types of pearls, including saltwater and freshwater varieties. Learn about their sources, including Japan, Cook Islands, Mexico, and China, and understand the factors affecting colour and quality. Find out about pearl formation, and learn to differentiate between natural, cultured, and imitation pearls. Gain insight into how X-ray imaging and the ‘tooth test’ can help identify these gemstones.

You will be empowered to better appreciate the allure of pearls in the world of jewellery and make informed decisions when purchasing pearl jewellery.

The digital handout for the first Section “Pearls: Natural, Cultured and Imitations” is available for download in the Materials tab above.

In this final lesson, learners will discover the importance of proper care and cleaning for their diamond jewellery. Diamonds have a natural affinity for grease, which can accumulate from the use of creams and lotions. This build-up of grease can affect the way diamonds react with light and lessen their brilliance.

To ensure that their diamond jewellery remains in top condition, learners are encouraged to clean their pieces approximately once every two weeks or at least once a month. The lesson covers the simple, effective method of using a bowl of water, mild non-detergent soap, and a soft brush (like a baby toothbrush) to clean the jewellery thoroughly. This process is easy, fast, and requires no additional equipment.

Though ultrasonic cleaners can be effective for cleaning gold and diamond jewellery, they can also be dangerous for other types of gems and materials. The lesson advises caution when using ultrasonics and provides an alternative method to maintain the beauty and longevity of their treasured pieces. By following these proper care and cleaning techniques, learners will be able to preserve the brilliance and shine of their diamonds and ensure they remain as beautiful as possible.

In this lesson, learners will gain insights into the importance of gemstone certificates and how to read them. They will understand that certificates have become increasingly important in the gemstone and diamond industry, providing detailed information about a stone’s attributes, such as cut, colour, clarity, carat weight, and more.

Tanja will highlight the differences between various well-known gemmological labs, emphasizing that different labs may grade stones differently due to their unique systems and terminology. Buyers are encouraged to seek certificates from reputable labs recognized worldwide.

The lesson also covers the various elements found on certificates, including registration numbers, laser inscriptions, measurements, proportions, grades for cut, polish, symmetry, clarity, and colour with examples of different certificates from various labs. Finally, Tanja will share an interesting story demonstrating how different labs can yield different results and emphasizes the importance of trusting the lab issuing the certificate.

In this lesson, learners will discover various diamond treatments that can enhance the appearance of diamonds. The lesson covers laser drilling, which was invented in the late 1960s to lighten dark inclusions in diamonds, making them less visible to the naked eye. Participants will also learn about fracture filling, a technique similar to oiling emeralds that helps make fractures in diamonds less evident.

The lesson delves into the complex process of diamond colour change, involving irradiation and heat treatment, ultimately producing a range of beautiful colours. In addition, learners will explore high pressure high temperature treatment, which can transform brown diamonds into more desirable colours like green and yellow.