Milestones in the early history of diamonds and diamond cutting:
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Blue diamonds are extremely rare, exquisitely beautiful, and rich in old folk lore. This special combination has made them coveted by diamond lovers and jewelry connoisseurs. How rare are blue diamonds? To find that glittering needle in the haystack, tons of ore have to be unearthed. And when a blue diamond is found, you can imagine the excitement it causes. But what make a blue diamond blue? The answer is a diamonds exposure to either Boron, Radiation or Hydrogen. The presence of boron impurities is most often responsible for the colour of natural blue diamonds. The centre photo below shows a natural blue diamond with boron impurities. Some blue diamonds are naturally coloured by exposure to radiation. These diamonds usually appear with a more vivid green-blue colour. Diamonds coloured by their association with hydrogen are described as gray-violet to gray-blue (pictured below on the right). Blue diamonds were first found in India and were brought to the West by the gem dealer Jean-Baptiste Tavernier in the 17th century. He sold a very large blue diamond to King Louis XIV of France. The diamond was originally known as the Tavernier Blue but when re-cut to become a part of the French crown jewels it became known as the French Blue. The diamond was stolen in 1792 and re-cut to avoid detection and was then eventually purcahsed by Henry Philip Hope in 1830. Since being purchased the diamond gained the reputation of being cursed and has often been thought to be associated with the deaths of very difficult lives of some of its owners. This diamond is now known as the very famous Hope diamond and is now housed in the Smithsonian Natural History Museum in Washington, D.C. Another historically notable blue diamond is the 70.21 ct Idol’s Eye. This diamond was probably found in India’s Golconda district sometime in the early 17th century, but its first historic record was its sale to a mysterious buyer at Christie’s London on July 14, 1865. In 1906, it was known to be in the possession of Abdul Hamid II (1842–1918), the 34th Ottoman Sultan. India was historically the source for blue diamonds but within the last several years, notable blue diamonds have been found at the Cullinan Mine in South Africa. A few other South African mines have produced blue diamonds and some are occasionally found in Sierra Leone, Borneo - which is off the coast of Indonesia, and Brazil. Blue diamonds are absolutely beautiful but they do present unique cutting challenges. The rough diamond is usually asymmetrical which can make it more difficult to determine how the stone should be cut and polished. Rough blue diamonds can also have colour zoning – areas that have more blue than others. Cutters want to get the best even colour out of a diamond, while retaining as much weight as possible, and colour zoning can make this balancing act extremely difficult. With understanding of a subject often comes a deeper appreciation. Now that you know some of the secrets of blue diamonds, you may find them even more beautiful.
GIA’s online Gem Encyclopedia has an entire entry devoted to coloured diamonds. Thanks to GIA Blog for this fabulous article and photos! http://4csblog.gia.edu/ As I have previously blogged about colour is one of the four c's that you should consider when you are purchasing a diamond. The majority of you will understand the GIA colour grading scale which rages from D - Z. D being the very best colour or colourless and Z being at the opposite end of the scale showing a yellow or brown tone and saturation.
But how do we actually view colour in a diamond? When light enters our diamond a process called selective absorption occurs. Selective absorption is what offers colours to all things. With diamonds it does this when visible white light enters the diamond enabling the gem to absorb some of the wavelengths, while also transmitting wavelengths to the viewers eye. Absorption bands or lines in the spectrum of of an incandescent source are seen through the absorbing medium - the diamond. If little or no colour is absorbed by an object then it appears colourless or white. On the other hand if the entire spectrum of colours is absorbed, the object will appear black. In-between there are an infinite number of colour possibilities. In diamonds it is the presence of nitrogen atoms (or other atoms of impurity) which determines the level of absorption, and therefore the color of the diamond. The less impurities there are in your diamond the whiter or more colourless it will appear. D colour diamonds are very rare but we specialize in providing our clients with these very rare GIA certified diamonds. For some people buying a diamond is not just about choosing a ring at your local jewellery store. The inter-web has enabled education about absolutely everything on a whole new level and we can now
delve into the depths of diamond data and discover for ourselves exactly what makes a diamond tick, or sparkle! Diamond Anatomy plays a major role in how beautiful a diamond appears, and choosing a diamond with at least very good symmetry or cut is something that can not be emphasized enough. No matter the colour or clarity if the cut is poor the diamond will not sparkle. This is because diamond cutters have over time perfected what proportions enable maximum light refraction which is what makes a diamond sparkle. So why aren't all diamonds cut with at least a very good cut? The answer to this is a little complex. Whilst we who are selling diamonds would love for all diamonds to have perfect or near perfect proportions it is the job of the diamond cutter to look at each individual stone and decide what is going to be best acheived with this particular one. It may be that a heavier carat weight will be achieved by increasing the pavillion depth of the diamond, and in turn this may mean a better price for the stone when it goes to the diamond market. A half carat diamond will always achieve a better price than a 0.45ct regardless of the diamonds proportions. Consumers do pay a premium for very good quality diamonds. But buying GIA Certified diamonds does ensure you know all about your diamonds specifications and anatomy and at NZ Diamonds we strive to provide the very best diamond prices that we can for very good quality diamonds. The Gemological Institute of America have excellent information available on their website to teach you all about diamonds, below is everything you need to know about Diamond Anatomy and by clicking on the picture above you can be referred to their website for even more in depth diamond data. Table Size: The table is the top horizontal facet of the diamond. The average table size is expressed as a percentage of the diamond’s average girdle diameter. While an ‘Excellent’ grade diamond will have a table size between 52 and 62 percent, other proportions are important too. Remember that GIA doesn’t consider individual proportions in isolation. Total Depth: The diamond’s overall depth from the surface of the table to the culet, expressed as a percentage of the average girdle diameter. Pavilion Depth: The pavilion is the lower portion of a diamond from the bottom edge of the girdle to the culet. The pavilion depth is expressed as a percentage of the average girdle diameter. A pavilion depth that’s too shallow or too deep will allow light to escape from the side or bottom of the stone. A well-cut diamond will direct more light upward through the crown. Pavilion Angle: Pavilion angle is another important dimension of the stone, especially as it relates to a diamond’s brightness. It is the average of the angles formed by the diamond’s pavilion main facets and its girdle plane. This should fall between 40.6 and 41.8 degrees to be considered “Excellent,” providing other parameters also fit their proper ranges. Crown Height: The crown is the upper portion of the diamond, from the top edge of the girdle to the table. The average crown height is expressed as a percentage of the average girdle diameter. It can affect both the dispersion and brightness of a diamond. Crown Angle: The crown angle is the angle that’s formed where the bezel facets meet the girdle plane. The crown angle in a well-cut diamond will be within 31.5 to 36.5 degrees. The crown angle has a large effect on the face-up appearance of a round brilliant cut diamond. The best range of crown angles provide a route for exiting light dispersion, as well as additional contrasting directions for entering light. Star Length: The horizontally projected distance from the point of the star facet to the edge of the table, relative to the distance between the table edge and the girdle edge. A well-cut diamond will range between 40 to 70 percent, when other parameters are within the correct ranges Girdle Thickness: The girdle is the middle portion of a diamond, a narrow section separating the crown from the pavilion, and functions as the diamond’s setting edge. The girdle thickness is described as a range from its thinnest to thickest areas. A thick girdle is less desirable because it unnecessarily adds weight to the stone where it matters the least (making the diamond appear smaller). An extremely thin girdle is sometimes referred to as a knife-edge, and results in a diamond that is more fragile and susceptible to chipping. Therefore, a girdle that is “medium to slightly thick” is preferred. Lower Girdle / Half Facet Length: This ratio is measured by calculating how long the lower girdle facets are relative to the length of the pavilion. This defines the contrast of a round brilliant cut diamond, which controls the brilliance of a diamond. The well-cut diamond will range between 65 to 90 percent. Diamonds with longer lower half facets will have a little more scintillation. Culet: The culet is the small facet at the bottom of a diamond intended to prevent chipping and abrasion to the point. The culet size can affect face-up appearance and it’s described as the average width of the facet. Size is expressed as none, very small, small, medium, slightly large, large, very large, and extremely large. When there is no culet, it is sometimes referred to as a pointed culet. Preferably the culet will not be visible with the unaided eye, and when described as none (no culet), very small or small on a GIA report, it falls in the excellent range. |