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Kerrie Ann McNaughton
11th January 2010 11:36

Gemstone Cutting

 

Hi All

I hope you all had a wonderful Christmas and are all set for the year ahead.

Working as a jewellery designer we come across many wonderful gemstones to suit each individual's personality and style, but do you know how much history your piece of jewellery has to it before each of you wear it? Your piece of jewellery has a story to tell from mining of the metal and the gemstones to the highly skilled craftsmanship of the goldsmith through to the wearer's joy of displaying this piece throughout many many years of enjoyment. I feel it's wonderful to know some of the processes your piece of jewellery has undertaken before you see the final product, as there are so many stages. Let me take you through one of the techniques I particularly find of interest, gemstone cutting.

Gemstone cutting is a very highly skilled process which is named Lapidary. The lapiderest practices the very fine art of the forming and finishing of the stones which are worked into beautiful gemstones that are then made into a variety of jewellery. The process of cutting precious gemstones and diamonds is quite different, due to the very highly specialized techniques required to produce the perfect proportions and dimensions needed for a successful brilliance of all diamonds. I will be going through this in more detail with you all in my next blog.

As you can see below the gemstone is mined in a very rough form, from this point this particular raw material undertakes many process before the stone is ready to be sold.

Watermelon Tourmaline

The purpose of a lapiderer is for them to choose the best way to cut the particular raw material to enhance its natural beauty and brilliance, for example if the crystals were clear then this will make a very successful piece of material for faceting where as some of the materials have interesting striations or inclusions such as slender like needles of rutilite or tourmaline which would be famously cut into a cabochon to enhance these features, these stones will not necessarily make successful faceted stones as there would not be enough light entering the stone to accentuate the sparkle.

Quartz pendant
Quartz pendant

You will find that all rough precious and semi precious gemstones excluding diamonds all go through very similar techniques, to name a few, sawing, grinding, sanding, lapping, polishing, drilling, and tumbling. These gemstones will be cut by a piece of material which is a lot harder than the stone, usually diamond. Lapidarists will also use some manmade compounds, made up of silicon and carbon, producing a hardness of 9.5, harder than all of the gemstones that are to be cut.

Sawing

The gemstone starts as a raw mined material which can be seen here:

Rough Stone
Rhodochrosite

Many gems are near useless to the gem cutter unless they are sectioned into pieces small enough to be cut further by the lapidary process. These are cut by a thin circular blade which will be made from steel, copper or a phosphor bronze alloy where you will find that the outside edge has a diamond grit. Once the wheel rotates it will start to scratch away at the rough gemstone, within this process it is very important that a liquid in the form of either water or oil is used which will protect the blade from overheating and wash away the loose cuttings. There are many saws used by Lapidarists, such as a slab saw used for cutting the stone into thin piece, a trim saw for cutting stones on a much smaller scale, and a faceteer saw which is commonly used for the more expensive rough gemstones.

Cutting and Grinding

Grinding the raw material is the next stage the stone goes through. This is where the material is grinded to produce a very rough form; again it is also important that either water or oil is used during this process. There are two grades the stone will go through, the first with a coarse diamond or silicon abrasive for rough forming then a much finer grade which will produce the more accurate shape and sanding. The same wheel will be used to form the rough shape for faceted gems, grinding bevels on flats, shaping carvings and profiling pieces for inlay work.

Stone cutting

Sanding

Sanding is one of the final stages the stone goes through before the final polishing takes place, very similar to grinding the stone, it will go through finer grades of abrasive which will create a very smooth surface in preparation for final polishing. By sanding the stone this will allow the Lapidarist to be in more control of the final shaping. For stones with rounded surfaces a belt sander is used to avoid creating flat areas on the domed stones.

Lapping and Faceting

Lapping is the final process a gem has to go through before final polishing. Lapping is very similar in process to grinding and sanding, the main difference with this technique is that only one side of the disc is used (which is formerly known as the lap) this will then create many flat surfaces on this stone which will then start to facet the gem itself. The stones used for faceting will be clear stones where the flat sides will be cut into the surface to enhance the maximum brilliance and sparkle to the stone. The stone is set into a piece of wax positioned on a rod which will allow the Lapidarist to have the maximum amount of control as this is a very crucial part of the cutting itself. Once one of the facets has been ground sanded and polished on the lapping wheel the jig is then adjusted ready for other facets to be applied on another part of the stone.

White and rose gold spinel engagement ring
Platinum and tanzanite engagement ring

Cabochons

Cutting a cabochon stone is be quite different to the above technique, it is said to be one of the simplest out of the lapidary processes. As mentioned above, stones that are cut into a cabochon will be stones that are often an opaque rough material. The cabochon is normally formed throughout the grinding and the sanding process.

White gold and plum tourmaline engagement ring
White gold pear shape garnet engagement ring

Tumbling

Tumbling will be used for a vast number of gemstones to be sanded down and polished all at the same time. This is a machine in which turns at very low speeds with abrasives and water for often days and weeks. While tumbling with finer abrasives each of these stones will become gradually smoother until they finally become polished.

Polishing

Polishing is the final stage. The stone is polished with very fine grades of diamond which will polish any form of material. Other materials are also evident within this process such as, aluminum oxide, cerium oxide and ferric oxide. Ferric oxide is the red oxide of iron/rouge which is a polishing compound, popularly known within the jewellery industry, it is similar in composition to hematite, seen as a dark brown reddish in colour. Finally the last compound to be used is silicon dioxide known as Tripol, again another polishing compound which will is used by our goldsmiths when a piece of jewellery is going through its final polishing stages.

Polishing

So this is just an overview of one of the elements your wonderful, precious gemstone has undergone before it reaches you all. In a few weeks time I will tell you a little bit more about how a diamond is cut.

I would like to wish you all a very happy new year.

Best wishes, Kerrie - Ann

Kerrie Ann McNaughton
 

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  • Harriet Kelsall Jewellery Design, North Barn, Fairclough Hall Farm, Halls Green, Weston, Hertfordshire, SG4 7DP, England
    Phone: +44 (0)1462 790565 Fax: +44 (0)1462 790140 enquiries@hkjewellery.co.uk
  • Harriet Kelsall Jewellery Design, 6/7 Green Street, Cambridge, Cambridgeshire, CB2 3JU, England.
    Phone: +44 (0)1223 461333 Fax: +44 (0)1223 365269 cambridge@hkjewellery.co.uk

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