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Diamonds-Dia Grading
Diamonds-Dia Grading Chapters 19 and 20.
| Term | Definition |
|---|---|
| Memo | Buying agreement where a dealer entrusts merchandise to a customer for inspection and approval without requiring imme- diate payment. |
| Price Lists in General | you need to know how those estimates relate to prices in your market.Some price lists are based on actual recent transactions, while some are based on what dealers agree is a price at which any of them would sell, called the high asking price. |
| Price Lists from computer trading networks, bourse or diamond exchange | Other price lists use the selling prices from computer-trading networks, and some are based on the prices paid in a bourse, or diamond exchange. The publisher of each list usually states which market the prices are based on and how the figures were derive |
| Rapaport Diamond Report Price List | The first successful price sheet, the Rapaport Diamond Report, lists the “approximate high asking price” in New York. |
| High pressure, high temperature (HPHT) | Diamond synthesis method that mimics the pressure and temperature conditions that lead to natural diamond formation. Most HPHT synthetic diamonds are yellow or brown because they contain nitrogen impurities |
| Why have scientific advances made synthetic diamonds better for industrial use than natural diamonds? In many cases, synthetic diamond grit outlasts natural diamond grit because of its uniformity | manufacturers can control the growth process. Unlike natural diamonds, which nature fashions randomly, synthetics can be turned out in predictable shapes and sizes. Manufacturers can also control impurities and other aspects of quality. |
| Chemical vapor deposition (CVD) | growth of synthetic diamond from carbon-rich gas in thin layers onto a silicon or diamond surface.Advances have led to production of attractive gem-quality stones. CVD synthetic diamonds lack the flux metallic inclusions found in HPHT synthetic diamonds. |
| A trained gemologist can readily identify most HPHT synthetic diamonds using standard gemological instruments and three basic procedures: | Examining the diamond with a microscope, looking for inclusions, color zoning, and graining • Checking the diamond’s fluorescence under ultraviolet (UV) radiation • Checking the diamond’s reaction to a magnet |
| Synthetic diamonds don’t have the same variety of mineral inclusions that natural ones do. A synthetic diamond won’t contain included minerals like garnet, diopside, or even another diamond. What might they contain? | Dark, opaque remnants of the metallic flux need to be examined closely. You can use fiber-optic light to determine if they’re highly reflective or metallic looking. An inclusion of metallic flux is evidence of a synthetic diamond. |
| DETECTING CVD SYNTHETIC DIAMONDS | They might contain small, irregularly shaped, black inclusions that are probably graphite. The stones lack the flux metal inclusions common in synthetic diamonds grown by high- pressure synthesis. |
| Detecting HPHT Synthetic Diamonds | Can be identified by their metallic flux inclusions, growth structures, and fluorescence. Because synthetic diamonds grow in an iron-based flux, they contain many metallic inclusions. Some have so many metallic inclusions that they respond to a magnet. |
| Linear accelerator | A machine used to accelerate electrons to high energy along a straight path. |
| Irradiation | Exposure of a material to radiation; causes color change in diamonds.Natural radiation in the ground makes the diamonds near it turn green |
| Where do diamonds get their yellow color from? | The diamond color comes from the presence of impurities or the effect of distortions or defects in a diamond’s crystal lattice. Diamonds tend to be yellow when nitrogen is present as an impurity. |
| Where do diamonds get their blue color from? | The diamond color comes from the presence of impurities or the effect of distortions or defects in a diamond’s crystal lattice. Diamonds tend to be blue when the impurity agent is boron and a conductor of electricity. |
| Where do diamonds get their green color from? | Green diamonds get their color when radiation displaces atoms from their normal positions in the crystal lattice. |
| Where do diamonds get their pink or brown color from? | The diamond color can come from the effect of distortions or defects in a diamond’s crystal lattice. Pink or brown colors are due to graining, an irregularity or defect in the crystal that occurs during growth. |
| Linear Accelerator | The first irradiated diamonds were treated in a cyclotron, a large device developed for atomic research. Today, most diamond treaters a linear accelerator—A more compact machine used to accelerate electrons to high energy along a straight path. |
| Graphitization | Graphite formation around a diamond’s mineral inclusions and feathers that results from the extreme conditions of HPHT processing |
| Half-life | The length of time required for half of a group of atoms of a particular type (radioactive) to decay into another type (non-radioactive). |
| Modern diamond irradiation methods | leave little or no color zoning and no radioactivity. |
| Fracture filling | is the most common diamond treatment.Some signs of fracture filling are the flash effect, trapped bubbles, and a crackled texture. Disclosure of fracture filling is an industry requirement. |
| Laser Drilling | LD can make a diamond more marketable by improving its appearance by using a beam of laser light to reach a dimaond's dark inclusions and disguise or elimainate them. As laser drill-holes are permanent, gem labs report them as clarity characteristics. |
| HPHT | HPHT eliminates the structural distortions that cause brownish coloring in some Type IIa diamonds. HPHT can dramatically improve the color and value of brownish diamonds. |
| Heat can alter irradiated colors | Annealed diamond color can change if it’s exposed to heat during routine repairs. |
| Treated diamonds vs synthetics in the marketplace. | There are far more treated diamonds in the marketplace than synthetic diamonds. Although synthetic diamonds are grown widely for industrial uses, it’s still too costly and time consuming to produce synthetic diamonds on a wide scale for use in jewelry. |
| Internal Laser Drilling (ILD), a variation on laser drilling. | It’s a technique that uses a laser to expand an existing cleavage or create a new cleavage between an inclusion and the surface and allows the introduction of a bleaching solution. The result is the lightening of a dark inclusion, making it less visible. |
| WHY Internal Laser Drilling(ILD? | The cleavage created by this procedure is more natural-looking than a traditional laser drill-hole.Under the microscope, you’ll see a step-like series of tiny cleavages. These wormhole-like channels are definite signs of ILD treatment |
| Most origin-of-color tests should be done by a gemological laboratory. T or F? | True |
| Coatings were one of the earliest methods of diamond color modification, but they fell out of use when more advanced techniques like HPHT emerged. | This changed in recent years with the intro of a new coating method. Modern silica coatings result in a variety of natural-looking fancy colors, including pinks, oranges, yellows, blues, and violets. |
| Downside of modern silica coatings? | These coatings are fairly durable, but not permanent. This means that detection and disclosure are vital when handling coated color-treated diamonds as the can be damaged by heat and chemicals used in jewelry repairs and can scratch fairly easily. |
| Annealing - A controlled heating and cooling process is another way to change diamond color. | When it follows irradiation in a two-step process, annealing modifies irradiated colors to produce brown, orange, or yellow. Rarely, it can also produce shades of pink, red, or purple. |
| Annealing is also sometimes used alone. | The process changes diamond colors in a series—generally blue to green to brown to yellow—and the treatment is stopped when the desired color is reached. |
| Annealing and reprecusions of heat used in later repairs | As with irradiation, if heat is later applied to an annealed diamond during routine repairs, it can drastically alter its color. |
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jlgulledge