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Cut GemIan Robinson - Bespoke Gems
Precision Cut in the UK
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Sapphire and Ruby

Same stuff - both being techically called corundum - crystalline aluminium oxide. Sapphire can be any colour - not just blue, however if blood red it is called ruby. Sapphire is very hard, one is unlikely to scratch sapphire so it is good for rings or jewelry likely to take the occasional knock or scrape. A nice material to work with, usually straightforward if slow to cut and takes a bright polish.

Spinel

The ruby or sapphire imposter, magnetium aluminium oxide MgAl2O4. Spinel has been rather underrated though is now growing in popularity. Its optical properties so similar to sapphire that before sophisticated analysis they were confused. Indeed the world's best known ruby is probably The Black Prince's Ruby, the centerpiece of England's state crown. This is however not ruby but a large spinel. Natural spinel is quite expensive though not as steep as sapphire. Again it is also available lab-grown in a range of colours. Cuts and polishes very much like sapphire.

Lab Created vs Natural Sapphire and Spinel

Almost all sapphires offered in the U.K. were grown in a lab rather than in the earth!

If you look at a sapphire and the stone is obviously internally flawed then it is likely natural. If the stone is perfectly clear it is almost certainly lab-grown. It is real, genuine sapphire i.e. crystalline aluminium oxide - but the rough was manufactured. Price is little help, I trawled around jewellers recently looking at sapphire pendants up to £10,000 - these were all lab grown and generally not well cut.

Cutting natural material is little different from lab-grown and takes a similar time. However many customers buy stones by weight rather than quality.

Some numbers

Say one has 15ct (3g) high quality natural sapphire costing £2500. If I cut this for optical quality I would be doing well to only waste 2/3rds. The final stone would at best weigh 5ct – depending on quality this would sell for, say £4-5,000. An artisan jeweller may charge £500-£1000 to produce a unique custom setting. This would then retail for £10,000-£25,000 in a shop.

If you are looking at spending over £500 I would recommend finding a stone you like then a silver or goldsmith to design something tasty.

However .. back to the rough. I could choose a cut that produced a 7 or 8 ct stone. Optically this would be less good, typically dumping light out of the pavilion rather than reflecting it back to the eye resulting in a less bright, duller, stone. Lacking somewhat in ‘twinkle’.

Unlike the US, Australian or the far East the UK does not have a local gem mining and cutting industry and many customers will buy simply by weight. A 7 or 8 ct stone, even sub-optimally cut will likely sell for more than a well-cut 5ct. With very expensive rough one is encouraged to cut less optimally.

Lab grown sapphire and spinel are real, they are chemically identical to natural stones. They are almost flawess and the highest grade – which I use, from Deja, Switzerland costs approx £1000 kg-1. Chemically and optically identical to natural rough there is no temptation to ‘cut for weight’ and I am happy to sacrifice 80%+ of a piece of rough in order to produce an optically superb stone.

What about other lab growns?

I don’t cut lab-grown quartzes as the price of good quality natural rough is sufficiently low to avoid compromises in cutting. One can still pay £100 for a good quality 20ct amethyst though.

I do have an interest in cutting 'lab-exotics', crystalline metallic oxides that do not occur in nature. For example I am lucky to possess 3 pieces of Lithium Tantalate - LiTaO3, an exotic optoelectronic crystal produced for the soviet defense industry in the late 1970's. Very rare with a high refractive index (2.2) similar to that of diamond and crazy high dispersion - three times diamond's.

Quartzes

People often go 'urghh' when thinking of quartz gemstones. However natural quartz, SiO2 comes in many different colours and goes by even more names including; Amethyst, Blue Moon Quartz, Citrine (lovely yellow colour), Ametrine, Rose Quartz, Smokey Quartz, Aventurine, Chrysoprase, Prasiolite, Rose de France, Rutilated ......................................

Whilst one can pay a fair wack for high quality rough I have not seen the need to use lab-grown alternatives. Natural quartz with a moh of 7 is softer and quicker to cut than sapphire but still hard enough to resist scratching in most settings. Takes a nice polish using oxide abrasives rather than diamond.

I do like cutting quartzes, one of my goals is to successly cut & polish a rutilated quartz with a single spike of rutile reflecting around inside. The rutile strands, TiO2 make it very tricky to polish.

Fluorite

What??... A spectacular mineral widely available in a range of colours. Tricky to work with and too soft for most jewelry unless the setting protects the stone. Facet fluorites are usually sold to collectors rather than for setting. .. I have some lovely blue rough that I keep looking at...