FACETING FOR INCLUSIONS

July 24, 2017

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 inclusions, not that many people will get to see a real life example. But rutilated quartz would just be plain quartz without the rutile needles, and a multitude of different minerals can make attractive inclusion scenery in quartz. Some inclusions are so characteristic of their host material, that examples without them are rare. Lily-pad inclusions, small disc-like cracks around minute black inclusions in peridot, are a good example.

Undesirable inclusions that cannot be removed by pre-forming often can be hidden partially beneath crown main and break facets. Avoid having these placed in the centre of a stone, where they will be multiplied by reflection in the pavilion facets. The very worst place to allow an undesirable inclusion to lurk is in the culet, so remove any damaged or cracked ‘skin’ from your rough before blocking out the pavilion main facets. Fine tubular inclusions, often seen in aquamarine, can be orientated vertically in the stone to minimise their visual intrusion. Stones containing a multitude of finely dispersed inclusions may appear ‘sleepy’ or milky, like much rose quartz. Such stones can be cut into very beautiful gems with some crown facets left frosted to increase the contrast between them and polished surfaces.

Orientating to display desirable inclusions involves the inverse of hiding them. For example, many cutters search for years for that piece of quartz or topaz with a single needle of rutile or tourmaline to orientate vertically through the centre of the stone. This will produce multiple reflections if centred properly, but how do you get it dead centre? I am sure there are other possibly more elegant solutions to the problem but I roughly preformed the stone, used a drill with a ball burr to grind two small hollows in the opposite ends of the rutile needle, and clamped the stone between two pointed dops in the transfer block before fixing the stone to one dop firmly with lots of wax. Then I removed the other dop, replaced it with a face-plate dop, and proceeded as if doing a transfer. The result was a needle perfectly centred in line with the dop axis to cut a round brilliant. (Unfortunately in this instance the rutile needle was very fine, which compromise the result. Perhaps one should just drill a hole through a stone and fill it with dye . . .)

Orientating other desirable inclusions depends on their nature and the shape of the rough. Deliberate central placement will cause multiple reflections. Perhaps you want two dissimilar inclusions side by side. It often is a good idea to avoid having inclusions breaking the surface of the crown. The difference in hardness relative to the host could leave polishing hollows or raised bumps. Once, when cutting large facets on some rutilated quartz, I was frustrated by some of the straight needles actually pushing through the quartz and emerging slightly on the other side. This would have caused a polishing disaster. So, what to do? A drop of cyano-acrylate glue on either end tethered the needles so that the little projections could be removed in pre-polishing to avoid scoring the polishing lap.

So next time you are selecting rough, don’t automatically discard included stones. Think creatively what you might be able to do with them to enhance their appearance and increase their value by cleverly including the inclusions. All the gems in the illustrations were cut by Duncan Miller.

Centreing a rutile needle in the transfer fixture between two dops ground to points

A 17,77 ct scapolite from Merelani tanzanite mines, with unidentified inclusions like ink spots>/p>


Very rare helical inclusions in a 64,66 ct Brazilian aquamarine

 

 Hollandite inclusions in a 15,86 ct Madagascar quartz, cut to follow the original shape of the crystal


 

Synthetics

June 27, 2017

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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New Barite Occurrence at Rosh Pinah Mine – Namibia

May 23, 2017

Transparent to whitish barite mineralization was found in an orogenic late phase leached fault zone. It seems that some of the barites are pseudomorphs replaced by snow white baritocalcite. This replacement supposedly took place at an even later phase when calcium-rich fluids migrated through the formation. This theory is supported by the occurrence of floater quartz crystals in a pocket where, on the one side, the quartz aggregates display the luster of ‘bergkristall’ and are coated on t...


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The History behind the Mike Lurie Collection

May 23, 2017

The Lurie family lived in Bulawayo, Rhodesia/Zimbabwe, from 1951 to 1966. During this time Robert’s late father, Mike, worked as a manufacturer’s representative. His job took him by car all over Southern Rhodesia (Zimbabwe), Northern Rhodesia (Zambia) and Nyasaland (Malawi). Every now and again Mike would stop his car in the middle of the bush to take a break from the difficult, long distance driving. He would often notice something shining, or an agat...


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Working With Diamond

May 23, 2017

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

April 25, 2017

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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New Barite Occurrence at Rosh Pinah Mine – Namibia

March 25, 2017

Author: Gisela Hinder, Rosh Pinah Geo Center, Rosh Pinah, Namibia

e-mail: gisela.hinder007@gmail.com

 Rosh Pinah Mine is situated in the southwest of Namibia about 80 km east of Oranjemund. Rosh Pinah Mine became well known for its beautiful barites when a massive pocket of yellow to orange barite crystals was opened in 1989. It is said that these barites were the best ever found in Namibia.

In February 2017 new barite crystals were discovered at Rosh Pinah. Yellowish, unfortunately smallish, ...


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GARNET

March 25, 2017

Duncan Miller

Garnets are among the easiest gem materials to facet. They have no distinct cleavage, although some crystals have a parting that causes them to fracture into thin slabs. The rough often is in globular shapes, which is good for weight recovery. When choosing rough, avoid being fooled by fake material. Red glass is sometimes covered in adhering deceptive ‘grit’ to mimic natural nodules. Illuminated from behind or the side with a torch, the characteristic internal swirls and r...


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A Bit about Blue Lace Chalcedony

March 25, 2017

Jo Wicht

Blue Lace “Agate” is found on the farm Ysterputs 254 (meaning iron holes) in Namibia. The mine is located adjacent to the “Blinkpan” (shining shallow lake) which can be seen to the west of the B1 highway about 80 km north of Vioolsdrift and Noordoewer, which are the border towns on either side of the Orange River between South African and Namibia.

Blue lace is not a true agate, but a chalcedony (microcrystalline quartz) laid down in a series of wavy bands, which gives it th...


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The Beryl Family

February 24, 2017

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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