|
|
Jewellery Guides - Identifying and buying Cubic Zirconia (CZ) and Diamonds
|
 |
|
 |
Cubic zirconia (CZ) is the synthesised form of the rare mineral cubic zirconium and is widely used to simulate diamonds. CZ is a hard stone and optically flawless. The discovery of CZ is linked to 2 German mineralogists, M V Stackelberg and K Chudoba. In 1937 they encountered naturally occurring cz embedded in metamict zircon. Although noted in their research, it was not considered an important discovery until Soviet scientists demonstrated its value as a synthetic diamond, even though they were originally researching possible new materials for use in lasers. They published their groundbreaking research in 1973 and commercial production began 3 years later. It wasn’t until 1977 that cz was produced for mass consumption by Hrand Djevahirdjian SA, a Swiss company, with the trade name ‘Djevalite’. In the former USSR, CZ was marketed as ‘Phianite’ (also ‘Phainite’ and ‘Phyanite’) and in the USA as ‘Diamonesque’ by the Ceres Corp. Modern names include ‘Diamonique’, trademarked by QVC. Swarovski, the Austrian leaded crystal glass company took up production in the late 70s.
How can you tell cubic zirconia stone from a diamond?
The simplest answer is that it is very difficult to tell them apart using the naked eye. A reputable jeweller or seasoned gemologist would often use a combination of methods to determine the authenticity of a diamond. The first indication is the clarity of the stone, cz is often too ‘clean’ at first glance. If the stone is cz, when a jeweller examines it using some form of magnification, such as a 10-power jeweller’s loupe, the stone will have no apparent ‘inclusions’ within it, whereas diamonds are graded by clarity with ‘flawless’ diamonds being both rare and extremely expensive (as well as highly desirable). While CZ has less of the sparkle and brilliance of a diamond, it typically features more fire and flashes of colour. CZ is also more brittle than diamonds, measuring between 7.5-8.5 on the Mohs scale versus 10 for diamonds. They are also about 75% heavier than diamonds.
How Are Diamonds Graded?
The ‘quality’ of a diamond is determined by a number of different (graded) factors, including the 4 Cs: Cut, Colour, Clarity and Carat (Weight).
Cut
This the only one of the 4 Cs that is influenced by human hand. It is also subject to multiple meanings, sometimes used to describe the actual shape of the diamond. The characteristics of a good ‘cut’ include the proportion of width and depth which impact on the diamond’s brilliance: its ability to maximise light refraction and therefore its ability to appear whiter or brighter. A shallow cut diamond can appear lifeless, with light disappearing out of the base of the stone and a light will escape out of the sides of a diamond that is cut too deep. The ideal cut is one where light disperses back out of the top of the stone. Diamond cuts are graded in terms of their light return and can be described as: Excellent, Ideal, Premium, Very Good and Good. Taken into account are other criteria such as symmetry of the cut, the cleanness of the facets and the polish.
The cutting of a rough diamond into a facetted and polished gem-quality stone is a multi-step process that involves marking, cleaving, sawing, bruting and faceting. After a diamond is graded, it is passed to a marker who decides what shape the diamond should be when it’s polished, making an estimate of its weight and cut. At this stage, the diamond is then either cleaved or sawn, with cleaving (splitting the diamond along it’s grain by striking it) being done manually with a hammer and sawing - usually involving a laser nowadays. The next stage in diamond processing is bruting, where the rough is rotated on a diamond lathe, rounding the diamond into a conical shape. The final step is the faceting procedure, a very precise process often involving a cross-cutter who takes the bruted diamond and fashions the table, crown and pavilion facets and then passes the stone to the brillianteerer who fashions the final remaining facets and polishes the finished article.
Diamond Facets
The following facets are typical of the modern brilliant (round) cut diamond. There are 58 facets in total. The widest part of the diamond is typically the ‘girdle’, the top part is the ‘crown’ and the lower section is the ‘pavilion’. The point at the base of the diamond is the ‘culet’. The flat faces of a diamond are referred to as ‘facets’. The ‘table’ is the largest and most important facet - the topmost facet - usually a symmetrical octagon. The ’star’ are the 8 facets immediately surrounding the table, forming an 8 pointed star shape. The ‘kite’ or ‘bezel’ facets reach from table to girdle, sharing edges with the star facets and are shaped like 4 sided kites. The 16 crown facets running the circumference of the girdle are ‘upper girdle facets’, sharing an edge with the kite facets. Conversely, the 16 ‘lower girdle facets’ run around the pavilion side of the diamond, running parallel with the upper girdle facets. The ‘pavilion’ facets are 8 4-sided facets which run from the ‘culet’ to the ‘girdle’.
Diamond Shapes
Diamonds can be square, oblong or baguette shaped. Oblong diamonds are cut in ’steps’ which run parallel to the topmost facet. Baguettes are long and thin rectangular shaped diamonds. Emerald or octagon shaped diamonds are also ’step’ cut with corners mitred. Ovals lose some brilliance due to their imperfect proportions, with varying depth to diameter ratios. Marquise or navette (boat) shapes are a variation of the round brilliant cut and were named after the Marquise de Pompadour and commissioned by Louix XIV and have 56 facets. The pear cut is almond shaped with a brilliant cut, having exactly 58 facets. Often referred to as a teardrop. The Princess cut is a square cut diamond, featuring an adapted round brilliant cut arrangement of facets, typically cut with 76 facets. The round brilliant cut is approximately 60 years old and accounts for 75% of all diamonds sold. The brilliant cut comprises 58 facets, as discussed above. The Asscher cut diamond is a square version of the emerald cut featuring a pavilion cut with rectangular facets. Named after the Asscher Brothers of Amsterdam who developed the cut in 1902, as with the emerald cut, the corners of the diamond are clipped to create 8 sides. The radiant cut is either square or oblong with clipped corners and combines the classic emerald step-cutting with some of the triangular faceting of the round brilliant cut. Developed and patented by Henry Grossbard of the Radiant Cut Diamond Company in 1977. The cushion cut is sometimes referred to as a pillow-cut and is an antique cut that closely resembles the Old Mine cut of the Victorian era (with large facets) and the modern oval cut, giving the appearance of a rectangle with rounded corners. The trillion or trilliant cut is triangle shaped with a total of 31 facets, trademarked by the Henry Meyer Diamond Company of New York in 1962.
Colour
Diamond colour is graded by the diamond colour scale, a scale devised by GIA, the Gemological Institute of America in the 1950s. This scale defines and regulates the diamond colour spectrum. The GIA proposed that diamond colour grading should begin at ‘D’ for the most colourless of diamonds, to allow the possible introduction of ‘A’, ‘B’ and ‘C’ grades in the future. Colourless (Grades D, E, F), Nearly Colourless (Grades G, H, I, J), Faintly Tinted (Grades K, L, M), Lightly Tinted (Grades N, O, P, R) and Tinted (Grades S-Z).
In mineralogy, inclusions are any material that is trapped inside a gemstone during its formation. In gemology, it refers to a flaw within the gem, a void, fracture or foreign substance that is visible inside the stone. Black spots are carbon deposits and white spots are called crystals. Internal fissures are referred to as feathers and small spots are known as pinpoints. A cloud is a group of pinpoints, giving the appearance of a large inclusion. These minor imperfections are graded using 10 x magnification. The following grading system is the internationally adopted system: F (Flawless), IF (Internally Flawless), VVS (Very Very Small Inclusions: VVS1 and VVS2), VS (Very Slightly Included: VS1 and VS2), SI (Slightly Imperfect, Small Inclusions: Si1, Si2 and Si3), LI (Large Inclusions Visible to the Naked Eye: LI1, LI2 and LI3 or P1, P2 and P3).
Carat
The 4th of the 4 ‘Cs’ is carat. A carat is a unit of weight - not size as is popularly held. Carat is named after the carob bean. In times gone by, one carob bean was considered to equal one carat. In the Orient, rice was used: 4 grains of rice equalled one carat. In 1907 the carat was standardised at 200mg and the grain was standardise at 50mg, thus a 1 carat diamond is sometimes called a “4 grainer”. Sometimes a points system is used to weigh diamonds; 1 carat equals 100 points, therefore a 75 point diamond weighs three quarters of a carat. Thus 3/4cts, 0.75cts or 75 points all mean the same thing.
|
|
|
|
|
 |
Quick Find |
|
|
|
| 0 items |
|
|
|
|
|
|
|
|
|
|
| There are currently no product reviews |
|
|
|
|
Beauty Products
