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FACETIPS – A GEM CUTTER’S NOTEBOOK

by
Duncan Miller


The faceting articles published over the past few years in the Mineral Chatter have been compiled into a single 128 page document, available for download for those interested in saving all the articles together. To download the pdf file click here.

A 29,18 ct cuprite from Onganja, Namibia, cut by Duncan Miller and now in a private collection in Germany.


Showing category "Faceting" (Show all posts)

A GEM CUTTER’S JUNK BOX

Posted by Site Moderator Webmaster on Thursday, June 25, 2020, In : Faceting 

Duncan Miller

After several years, or after many years, a gem cutter lands up with a junk box. Mine contains disappointing stones abandoned in disgust and partly-worked stones that came over the years with various faceting machines and batches of rough. As a lock-down project I decided to see what I could make from the contents of the faceting junk box. (There are another two – one with cabochons and another with broken synthetics. You never know, you know…)

To make it something of a ...


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FACETIPS - AN ‘EPIDOTE’ ANECDOTE

Posted by Site Moderator Webmaster on Sunday, November 24, 2019, In : Faceting 
Duncan Miller

A few years ago, faceting friends of mine in Durban bought some green gem quality material sold as epidote or possibly peridot. It was nice clear green, and some pieces of rough still adhered to a matrix, "dug out of the ground right in front" of the vendor from Moçambique. The cutting and polishing was easy, apparently working like tanzanite. But the surface of the polished stone degraded quite rapidly, developing hazy spots, so samples were sent to me for identification.

The ...


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FACETIP – POLISHING REALLY TROUBLESOME FACETS

Posted by Site Moderator Webmaster on Friday, October 25, 2019, In : Faceting 

Duncan Miller

Polishing soft gem materials, Mohs’s hardness 5 and less, and facets near the cleavage of some harder materials can be very difficult with commonly used polishing laps. Some years ago, Gearloose Lapidary (www.gearloose.co) introduced the Lightside™ lap, intended specifically for polishing soft materials. It is a ‘reduced-friction’ composite lap, used with diamond or oxide slurry to produce flat facets without significant edge rounding. It is described as a ‘durable, p...


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My New Toy

Posted by Site Moderator Webmaster on Sunday, August 25, 2019, In : Faceting 

by Duncan Miller

A few months ago I bought an Imahashi faceting machine, Faceting Unit Model FAC-8C, the earlier of two models. This one dates from 1970, co-incident with when I started faceting. Sometime during the 1970s my father owned one briefly, but I took no notice of it then. Now it intrigued me, because it is a platform machine, unlike the more familiar mast machines. Platform machines have several attractive features. You can lift the entire handpiece free of the machine to inspect th...


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FACETIPS

Posted by Site Moderator Webmaster on Wednesday, July 24, 2019, In : Faceting 

By Duncan Miller

How to teach yourself faceting, in three easy steps:

1.      Acquire a faceting machine. https://facetorsguild.com.au/About-Faceting-Machines

2.      Learn to facet. https://www.gemsociety.org/article/lapidary-fundamentals-gemstone-faceting/

3.      Become an expert. https://www.youtube.com/watch?v=oD6ZlNmtwmM&list=PLFIMjYf_BtnvaVZNQkHJ4ieF-v1fqPgqu&index=2

These are good introductory lessons for those starting out faceting, and perhaps don’t have access to a mentor or ...


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Tanzanite

Posted by Site Moderator Webmaster on Monday, June 24, 2019, In : Faceting 
Duncan Miller

A tanzanite was re-cut last month by Duncan. The original stone was very lop-sided, with a shallow pavilion on one side, so there was considerable weight loss. The girdle is deliberately thick to retain weight and keep the finished stone over 5 ct.

 
14,6 × 11,1 × 7,3 mm; 8,67 ct before re-cutting



12,5 × 10,5 × 6,7 mm; 5,39 ct after re-cutting


...
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HYBRID DOPPING WITH WAX AND CYANOACRYLATE GLUE

Posted by Site Moderator Webmaster on Monday, June 24, 2019, In : Faceting 

Duncan Miller

Initial dopping requires a flat surface on your rough. Prepare a flat dop with a blob of hot wax on it and in the transfer fixture push this against another flat dop face to form a layer of wax a few millimetres thick. You can build this up with several layers if the stone you are going to cut is very heat sensitive. Clean the flat on your rough with alcohol. When the wax is cold, apply a small drop of cyanoacrylate glue (CA), position the rough on the dop quickly, and let the gl...


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Rhodochrosites

Posted by Site Moderator Webmaster on Friday, May 24, 2019, In : Faceting 

Duncan Miller





These are the rhodochrosites (presumably from Hotazel) that I have been faceting, on and off, for the past two months. The ‘pink’ stones (on the left) are 0,65 ct; 0,68 ct; 1,46 ct; and 0,96 ct.  The ‘red’ stones (on the right) are 1,39 ct; 1,66 ct; and 1,71 ct. The rough was acquired more than twenty years ago as a small batch of broken and half-finished stones. A recent article about faceted rhodochrosite in The Journal of Gemmology inspired me to try to resurrect them...


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WHO CUT THAT STONE, OR WHAT IS A GEM CUTTER WORTH?

Posted by Site Moderator Webmaster on Friday, May 24, 2019, In : Faceting 
Duncan Miller

The photograph here is of a magnificent 164,11 ct spodumene (variety kunzite) in the collection of the Smithsonian Institution, USA (https://geogallery.si.edu/10002906/spodumene-var-kunzite).


The accompanying text credits the mine at which it was found (in 2010 at the Oceanview Mine in Pala, California), the funds with which it was acquired (Tiffany & Co. Foundation endowment in 2012), and the photographer (Greg Polley). So who cut this stone? This is like acknowledging the ar...


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FACETIPS A simple Emerald Cut

Posted by Site Moderator Webmaster on Thursday, May 9, 2019, In : Faceting 

Duncan Miller

The Emerald Cut is not a meetpoint design so cutting stones with repeatable proportions and facet widths involves guesswork. The following sequence for cutting pavilion and crown avoids most of the guesswork and enables you to cut pairs or sets of matched stones. This sequence is modified from FACET DESIGN Vol. 4 by Robert Long & Norman Steel, in turn based partly on FACETING FOR AMATEURS by Glenn & Martha Vargas. This example uses 5° steps for the three pavilion tiers, but you ...


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FACETIP – QUARTZ

Posted by Site Moderator Webmaster on Thursday, February 21, 2019, In : Faceting 

By Duncan Miller

(This is a follow-up to a previous article on faceting quartz, to be found with other faceting articles on the club’s website http://ctminsoc.org.za/articles/category/Faceting.) 

Every faceter knows quartz, those great big glassy-looking chunks that seem to cry out to be turned into doorknobs. Or pretty, golden ‘citrine’ that can cut brilliant yellow stones. Or glowing, dark purple amethyst with seductive blue flashes, dreamy rose quartz, or rutilated quartz with geom...


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FACETIP – TOPAZ

Posted by Site Moderator Webmaster on Saturday, January 19, 2019, In : Faceting 

By Duncan Miller

Topaz is a rather under-rated gemstone. This perhaps it due to the fact that pure, colourless topaz is relatively plentiful. Much of it is irradiated and then heat-treated to produce various intensities of bright blue. Natural blue topaz tends to be much paler, although dark blue stones do occur naturally. These are rare and hence more valuable. Natural topaz occurs in a wide variety of colours, including light green, yellow, orange and pink. The famous orangey-pink topaz fr...


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FaceTips for December

Posted by Site Moderator Webmaster on Friday, November 23, 2018, In : Faceting 
by Duncan Miller

This month I will show you how to scale a GemCad diagram to a different L/W ratio. This is very easy if the diagram is a fully meetpoint diagram, without a preform. You note the initial L/W ratio from the Print Preview and then click on Scale in the Edit menu. Here you check the X box because you want to change the proportions in the X direction, then enter the appropriate numbers to divide by the initial L/W ratio and to multiply by the one you want, and press OK. The next me...


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FaceTips for November

Posted by Site Moderator Webmaster on Sunday, November 4, 2018, In : Faceting 

By Duncan Miller

I started faceting in pre-GemCad days and found cutting ovals very laborious. I would cut the girdles by eye, using various oval templates, and placed the brilliant-style facets by eye too. Producing matching pairs was very trying. The advent of meetpoint faceting and GemCad overcame all these difficulties. Now there are lots of designs for ovals that are meetpoint, requiring no preform, with the girdle outline evolving out of the cutting sequence. You can access some of the...


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FaceTips for October

Posted by Site Moderator Webmaster on Tuesday, September 25, 2018, In : Faceting 

By Duncan Miller

This was another jeweller’s request. The setter had broken one of a matching pair of blue-green stones, destined for earrings, bought by the client in India as emeralds. They were apatite; but nevertheless the broken stone had to be replaced to fit the already-made setting. Fortunately I had just one piece of blue-green apatite that matched the colour. In order to produce a stone of the same size and proportion I had to replicate the oval precisely. I could have slapped fa...


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FaceTips for September

Posted by Site Moderator Webmaster on Friday, August 24, 2018, In : Faceting 

By Duncan Miller

Here is a quick and easy oval with a standard 1:1.30 proportion. It has a fully conical pavilion, so you can spin a conical preform, stopping just short of producing a point. This means you don’t have to change angles and mast height when cutting the sixteen pavilion facets, which saves time and avoids mistakes. This is a fully meet-point design that doesn’t require a preform, so it would be good for a beginner’s first oval. It doesn’t work well in quartz or beryl, s...


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FaceTips for August

Posted by Site Moderator Webmaster on Wednesday, July 25, 2018, In : Faceting 

By Duncan Miller

Jewellers sometimes ask for the impossible, and it’s a challenge to try and oblige. This design was developed to cut the citrine for a dome-shaped ring. It had to be a ‘classical’ mixed cut with curved girdle lines to match the curve of the top of the ring. This design requires a preform to get the girdle facets the right size. The relative depth of the pavilion tiers affects the angles of the triangular corner facets, but these can b...


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Faceting

Posted by Site Moderator Webmaster on Monday, May 7, 2018, In : Faceting 

Here are two stones that Duncan Miller cut recently from rough he bought two months ago at Open Day. The yellow citrine (from Johann de Jongh) has only 58 facets, is 22 mm wide and weighs 37 ct. The design is ‘Xephyr’ by Arya Akhavan (yes, with an ‘X’). The light green fluorite (rough from Rob Smith), is the first one he has ever cut. It has even fewer facets, only 36, is 15,5 mm wide and weighs 16,2 ct. The design is slightly modified from ‘Six Shooter’ by the late Jeff Graham.  ...


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Faceting

Posted by Site Moderator Webmaster on Wednesday, January 17, 2018, In : Faceting 

 A magnificent 63 carat sphalerite from Aliva in Spain (http://gem-sphalerite.com/) cut by Duncan Miller. The design is Marco Voltolini’s “Superstarfish Dome 80”.

 

 A unique type of blue-green garnet has entered the gem market. The garnets reportedly come from a deposit near the border of Tanzania and Kenya. GIA’s Carlsbad laboratory obtained a small parcel of blue-green rough material and two faceted stones for examination. Unlike traditional blue-green garnets that exhibit a colo...


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Faceting

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

 

“Eye of the Storm” a faceting design created by Robert W. Strickland on 12th September 2017, in honour of those who suffered loss in the Caribbean hurricanes of 2017.

This design was first published in the United States Faceters’ Guild newsletter of September 2017.

When photographed directly into the centre of the culet, all the crown facets go dark, and the only light is in the “eye”, but viewed from other angles, the stone ...


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THE POLARISCOPE, THE FACETER’S FRIEND

Posted by Site Moderator Webmaster on Saturday, September 23, 2017, In : Faceting 

Duncan Miller

A polariscope consists essentially of two polaroid filters, or a source of plane polarised light and one polaroid filter. The source of polarised light can be a white computer screen or even the sky, viewed at 90 degrees to the Sun. For the filter, or analyser, you can use a sheet of polaroid, or a lens from a cheap pair of 3D movie spectacles.

Let’s start with a white computer flat screen. Even an older cell phone screen without a plastic cover produces plane polarised ligh...


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FACETING THE NAMIBIAN RARITIES

Posted by Site Moderator Webmaster on Thursday, August 24, 2017, In : Faceting 

Duncan Miller

During the 1974/75 university holidays I was fortunate to work for Sid Pieters in Windhoek for several months. It was a wonderful experience, including seeing some of the most famous mineral specimens then coming out of Tsumeb, but also to encounter some very special gem materials. Through Sid Pieters’s generosity I returned home to Cape Town with a few small fragments of jeremejevite from the original Namibian occurrence at Cape Cross and some pieces of cuprite from Onganja t...


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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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