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 Al2O3. 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.



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. I feel that the surface lustre of spinel exceeds that of sapphire. I do like spinel and have a perverse habit of cutting faceted stones in natural opaque black spinel.


Lab Created vs Natural Sapphire and Spinel

Many sapphires preset in jewellery were grown in a lab rather than in the earth! A reputable gemstone dealer will sell individual stones, personally guaranteed and likely authenticated by a reputable gemologist. You, the happy customer can then tootle-off and have your stone set by a jeweller in a custom setting.

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 quite possibly lab-grown. The only way for a customer to be sure is to have the stone authenticated by a gemologist.

Lab-grown 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 expensive sapphire pendants - to my eye these were all lab grown and generally not terribly 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.

Quality vs. Weight

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-£2000 to produce a unique custom setting. This would then retail for considerably more 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 £1500 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 well over £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.

I have just bought some lilac YAG, Yttrium Aluminnium Garnet from the same source - regarded by many as one of the most attractive of all exotics



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 etc.

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. Quartz can take a nice polish using oxide abrasives rather than diamond however can be tricky, i.e. very time consuming, to polished well. This may be one reason why quartzes are often specified as the material in gemsone cutting competitions.

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 difficult to polish.



Topaz, Al2SiO4(F, OH)2 is the hardest silicate with a moh hardnesss of 8, similar to spinel. It comes in a range of colours with blue being particularly attractive i.m.o. Natural Blue Topaz is very rare. Unless you dig it out yourself one must assume that all blue topaz has been made by irradiating natural white topaz. A very nice stone.



What??... Fluorite calcium fluoride, CaF2 is 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. Faceted fluorites are usually sold to collectors rather than for setting. I have some lovely blue rough that I keep looking at...


Spodumene - Hiddenite - Kunzite

Spodumene - Lithium aluminium inosilicate, LiAl(SiO3)2 can be a lovely looking gemstone. Kunzite being a pale lilac variety, Hiddenite a pale emerald green.

I have cut this taking suitable safety precautions i.e. ensuring my blood pressure medication is well stocked up. The stone is evil, very prone to fracture during cutting. It usually waits maliciously until you have just about finished after some 10-15 hours cutting before disintegrating on the dop. 'Kunzitite' being very similar to one of the words one shouts at this point. Life is too short.