Showing category "Faceting" (Show all posts)

FACETING FOR INCLUSIONS

Posted by Site Moderator Webmaster on Monday, July 24, 2017, In : Faceting 

Duncan Miller

Inclusions in gemstones often are seen as just a nuisance by faceters, who find themselves urged to buy only ‘clean’ rough. I suppose it is a matter of taste, but inclusions that do not detract from the visual appearance of a gemstone can aid in proving its authenticity. And some inclusions definitely enhance the value and appearance of certain gems. A visible ‘horse tail’ inclusion of asbestos fibres in Russian demantoid is perhaps the most famous example of desirable ...


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Synthetics

Posted by Site Moderator Webmaster on Tuesday, June 27, 2017, In : Faceting 

Duncan Miller

Synthetics are a wonderful source of relatively inexpensive faceting rough, in a wide array of colours, some of them not available at all in natural stones. On the whole, synthetic gem rough is predictable in its behaviour and also enables the cutter to explore quirky cuts in larger sizes than would be affordable in natural rough. And increasingly jewellers are setting well-cut synthetics in precious metal jewellery. So dive in, and enjoy yourself.

The most commonly available ...


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Working With Diamond

Posted by Site Moderator Webmaster on Tuesday, May 23, 2017, In : Faceting 

Duncan Miller

No, this is not about polishing diamonds, which in South Africa is illegal without a license, but about working with diamond grit or paste. For the coloured stone gem cutter, diamond paste is easier to source and to use. Loose grit and pastes are available in a range of mesh sizes, with crushed natural diamond or synthetic diamond. Synthetic diamond is made as single crystals and polycrystalline aggregates. The polycrystalline diamond breaks down with use to produce finer parti...


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TOURMALINE

Posted by Site Moderator Webmaster on Tuesday, April 25, 2017, In : Faceting 

Duncan Miller

Tourmaline can be temperamental. Rough tourmaline occurs in two distinct shapes – globular nodules and elongated pencil-like crystals elongated in the direction of the c-axis. The globular nodules sometimes spall concentrically, like onions, and the pencils sometime fracture transversely. This behaviour is difficult, if not impossible to predict, although fine cracks in the ‘skin’ of tourmaline pencils is not a good sign. The cracked skin must be removed by preforming or th...


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The Beryl Family

Posted by Site Moderator Webmaster on Friday, February 24, 2017, In : Faceting 

Duncan Miller

Many faceters recommend that beginners start with aquamarine. It usually presents no problems in faceting or polishing, is relatively easy to obtain, and in lighter colour it is not overwhelmingly expensive. Aquamarine is the blue or blue-green gem variety of the mineral beryl, an aluminium beryllium silicate. It occurs in elongated hexagonal barrel-shaped crystals. It is dichroic, with the most intense colour when viewed along the length, the so-called c-axis. This is a pity, ...


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Faceting and Polishing Quartz

Posted by Site Moderator Webmaster on Sunday, January 15, 2017, In : Faceting 

Duncan Miller

This is the first of an intended series of articles on faceting and polishing a variety of gemstones. I am beginning with quartz because that is what most people start faceting when they first take up the hobby. Quartz rough is inexpensive and readily available in a wide range of colours. It is not necessarily the easiest material to polish, but if a particular stone behaves badly it is no great loss to set it aside to be tackled at a later date. You should try to select rough ...


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Playing With Stars

Posted by Site Moderator Webmaster on Wednesday, November 23, 2016, In : Faceting 

I cut off the end of a damaged Goboboseb quartz crystal because it had a deep purple central inclusion at the one end, which I thought would make an interesting stone to facet.

 But then I noticed that the end of the remaining piece had regular purple stripes radiating from the centre to the points of the hexagonal crystal. So I cut off another section of the crystal to the depth I hoped I would need for cutting a gem.

I first tried to find the middle of the purple star shape, and marked s...


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THE C-AXIS, WHAT IT IS AND WHY IT IS USEFUL TO GEM CUTTERS

Posted by Site Moderator Webmaster on Friday, September 23, 2016, In : Faceting 
by Duncan Miller

All crystals fall into one of seven crystal systems, based on their symmetry. In crystal drawings, by convention, the c-axis usually is orientated vertically, in the plane of the paper. All crystals except those in the cubic (or isometric) crystal system have a c-axis. Cubic system crystals, like diamond, garnet and spinel, have no c-axis because all three crystallographic axes are necessarily the same length. In the other crystal systems the c-axis can be longer or shorter th...


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Selecting Rough

Posted by Site Moderator Webmaster on Saturday, June 25, 2016, In : Faceting 

By Duncan Miller

If you are going to facet, you need to learn something about mineralogy because you need to know what stones you should obtain, how their characteristics affect their behaviour while you are cutting and polishing them, and how they affect the optical properties of your finished gemstone. The easiest material for beginners to cut and polish is common red garnet. It presents no problem with cleavage or orientation for colour, and generally behaves itself well during ‘cutting...


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Re-polishing a Table Facet

Posted by Site Moderator Webmaster on Wednesday, May 4, 2016, In : Faceting 
Anyone who re-polishes worn stones, or who tries to remove a scratch from a table facet, will be familiar with a common problem. Some stones, in my experience particularly tourmaline, appear to develop a resistant ‘skin’ during polishing, which impedes the re-polishing process. The effect is that you cannot re-polish the facet, which just slides over the lap, with your usual polishing combination. I think it is due to work-hardening of a surface layer; but there are other opinions about w...
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Water Splash Covers

Posted by Site Moderator Webmaster on Thursday, March 24, 2016, In : Faceting 
To reduce water spray when facet cutting at high speed, use a splash guard cut from the lid of a cheap plastic bucket, or alternatively use a trimmed-down cake fruit mix bucket when cutting girdles on a Raytech faceting machine.


  
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Photographing Minerals & Gemstones

Posted by Site Moderator Webmaster on Monday, November 23, 2015, In : Faceting 
It is relatively easy to take acceptable photographs of mineral specimens.  Five years ago I photographed my Riemvasmaak fluorite collection for illustrations for an article published in Lapis magazine (Miller, D. 2010. Die Fluorite von Riemvasmaak, Südafrika – ein Besuch vor Ort. Lapis Mineralien Magazin April: 38-44).  These were taken with nothing more sophisticated than a cardboard box with cut-out windows covered with matt tracing paper in sunlight, and sloping black or white paper in...

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Cutting Cerussite

Posted by Site Moderator Webmaster on Tuesday, August 25, 2015, In : Faceting 

17 mm square, 55 carat cerussite faceted by Duncan Miller from rough provided by Rockey Ollewagen

Cerussite is lead carbonate (PbCO3) and probably the best crystals come from Tsumeb. These can be large and glassy, usually clear, but sometimes grey, brown or red. It has a hardness of 3½; a specific gravity of 6,5; distinct cleavage in two directions; is very brittle and extremely heat sensitive. The refractive index is high, at 1,90 to 2,07; and the birefringence very strong. The dispersion is...

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An unconventional Way of pre-forming “Doorstops”?

Posted by Site Moderator Webmaster on Thursday, July 23, 2015, In : Faceting 
I have an unfortunate tendency to cut “doorstops”, which in the faceting world means cutting a mighty big gem, such as the 50 carat amethyst shown here.


When a piece of rough asks to be cut into a gemstone, I always feel that I would like get the maximum-sized stone from the rough, regardless of a few inclusions, as they always add a bit of interest or a few additional flashes to the finished result.

BUT…….. cutting big pieces of quartz and not having any kind of pre-forming grinding wh...

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