Tag Archive | mohs scale

Turquoise, the friendship gem

The sun is out and we’ve been breaking out our summer jewellery, one of the most fabulous summer jewels is turquoise which might seem a strange choice, but it’s an excellent summer stone as the bright colour gives a great fresh look to nearly every outfit and faux turquoise jewellery is frequently found on the high street during the summer season (ok we admit it’s also a great choice in winter too – amazing contrast against black and in fairness it is December’s birthstone, so let’s agree that it’s an all round jewel).

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Turquoise is an opaque gem which has been valued by people for thousands of years due to its colouring.  It can be traced back as far as the Ancient Egyptians and Aztecs and is thought to have been introduced to Europe through Turkey, and it’s believed that this is how it was given its name.  Given it’s age there’s no surprise that myths and beliefs surround this gem, in ancient times it was thought that it could have some prophylactic uses (!) and that it changed colour to reflect the health of the wearer.  Whilst it’s true that Turquoise does turn green with dehydration and chemical reactions or treatments can change the colour even more,  as far as we know this doesn’t actually link to the wearer’s health…  Turquoise has also at times been believed to protect the wearer, and  has been used as both a talisman and holy stone.

Double Headed Serpent Turquoise Mosaic, the British Museum Collection

Double Headed Serpent Turquoise Mosaic, the British Museum Collection

What is clear is wherever you go in the world you are likely to spot a fair amount of Turquoise in their museum pieces, turquoise was often inlaid into both jewellery as well as building decoration, bridles, swords to name but a few.  Turquoise was even found in Tutankhamun’s tomb in his burial mask amongst other items, and famously examples can be found in the British Museum such as Aztec death masks.

Turquoise Mask, the Turquoise Mosaics collection, the British Museum

Turquoise Mask, the Turquoise Mosaics collection, the British Museum

Much admired, but often under appreciated in modern society, Turquoise has been much copied throughout the ages.  It’s fairly surprising that it has stuck around so long, particularly preserved ancient pieces, as it’s not one of the more durable gems.  Even the best turquoise is fracturable and on the Mohs scale it’s just under 6 at it’s hardest, similar to glass.  It’s also a porous gem and can be affected by reactions with other chemicals.

Turquoise is generally known as a fairly low value gem in today’s society, due to the prevalence of fakes or synthetics, and variety of available treatments means that it can be hard to tell what is real and what is not.  This uncertainty affects the price, as does the large influx to the market that synthetics bring.  However, this has not always been the case and it used to be held in high esteem by the Apaches of North America.  It was thought of as a particularly useful gem giving authority, protection and if given (rather than bought) can bring good luck (particularly on a Saturday…) and preserve friendship.

Examples of our own Turquoise are below, despite it’s structure and nature it can be faceted, it also takes a great polish and there are some simply stunning examples of cabochon cut Turquoise.  One of our favourite Turquoise pieces at the moment is this gorgeous Astley Clarke friendship bracelet.

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Turquoise has distinguishing inclusions caused by other minerals and metals being within the gem, but rarely it can be found without these, which is known as sleeping beauty turquoise.

Treatments

There are lots of treatments which can be applied to turquoise, and it is often treated to enhance its durability as in its natural state it is not particularly hard and suffers from being highly porous.  Other treatments are used to change the colour of the gem and there are some great examples particularly of purple turquoise.  Be warned if you are bothered about your turquoise being treated, whilst a gemmologist may be able to test to ascertain they type and occurrence of treatment, such tests are likely to damage your stone.

Some of the more basic treatments are waxing and oiling turquoise which enhances the colour and lustre of the gem, whilst these add to the appearance of the stone it can result in some discolouration over time if the stones are exposed to too much heat or sun.

Some turquoise is “stabilised” by having resin or plastic inserted into the stone under high pressure, this treatment is more stable than wax or oil so has better long-term results and can lead to otherwise unusable turquoise being brought up to gem quality.

Other treatments are more radical, such as reconstitution or “block” turquoise which is formed by bonding small fragments of turquoise with resin, or gluing thin turquoise onto another material to reinforce it which is known as “backing”.

Care

Whilst it’s important to take care of all your gems, the nature of turquoise, even when treated, means that chemicals such as oils, perfume or sun cream could lead to discolouration or damage of your stone.  The gem can dehydrate so try to keep away from strong sunlight for prolonged periods and store in a breathable material.  Due to it’s softer nature it’s also preferable to keep your turquoise away from items that could scratch it so a special section of your jewellery box or a pouch is a good idea to try and protect it.  Also bear in mind that it can’t be cleaned with the majority of jewellery cleaners, so when you take it off try giving it a gentle rub with a lint free cloth to keep it looking at its best.

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The colour of love?

As it’s July we thought we should do a quick shout out for July’s birthstone today (particularly as one of us is a July baby!)

Ruby spray

Ruby is a gem quality variety of corundum, and is essentially a red variety of sapphire.  Fine rubies are actually rare as they are formed when a soft limestone rock was put under extreme heat and pressure within the Earth’s crust, but more than that the limestone then had to come into contact with just the right elements, including chromium, which makes them relatively rare.

Due to the way they are formed all natural rubies have imperfections which include colour differences or markings, and silk, although this silk is an imperfection it is important to enable natural rubies to be distinguished from synthetic rubies.

Rubies reach 9 on the Mohs scale, which

The majority of us will identify a ruby simply because it’s red, but there’s actually more to this gem’s colour than simply one word.  As they are part of the sapphire family different countries take a different approach to colour identification, for example in the United States a minimum colour saturation must be met before a “ruby” becomes a ruby rather than a pink sapphire.  The ICA takes a more liberal approach, but it’s something you should certainly turn your mind to the issue of colour.

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 True or false?

Synthetic rubies are relatively common and were first created in 1937, by 1910 the annual production of synthetic rubies had reached 1000kg.  The fewer imperfections in a ruby the more likely it is to be treated with suspicion and identified as synthetic.  In addition to its use in gemstone jewellery synthetic ruby has use in industry as they can be used to make lasers or other production where it’s hard nature is useful.

What is interesting is that in addition to having to detect synthetic rubies, a number of imitation rubies are often found in the form of glass, or the genuine gemstones such as garnet and spinel.  The confusion between ruby and other gems has been a long standing issue, sometimes not helped by the use of some trade names such as rubellite, but one of the most famous examples of this confusion can even be found in the Crown Jewels!  A stunningly large spinel can be found on the Imperial State Crown, known as the Black Prince’s Ruby.

Myth & Legend

Back in time, as with many precious stones, people used to believe that ruby had powers to preserve the health of the wearer.  Particularly ruby was seen to help the wearer by changing colour when danger was close at hand, protect from poison and plague and even make the wearer invulnerable to steel weapons.  Ruby is absolutely surrounded by acres of legend, particularly stemming from the reverence it was given in South East Asia. and it’s definitely worth a read as some of the stories are interesting.  Star rubies were even more highly prized, it was believed that the star was formed by three benign spirits which had been imprisoned in the stone for a misdemeanour, the spirits represent faith, hope and destiny and it is thought that this type of stone can bring good fortune to the wearer.

Treatments

Due to their nature and the naturally occurring imperfections the overwhelming majority of rubies are treated before coming to the jewellery market.  The most common treatment is heating, but other treatments include colour alteration, fracture filling or dissolving silk defects within the ruby.  Heating can improve both the colour and silk within the ruby.  Fracture filling does what it says on the tin, essentially using lead glass (or similar translucent) to fill the cracks within the ruby, which improves the translucency.

Unlike with some gems the treatment can be observed through a 10x loupe, and the majority of treatments are acceptable due to the nature of natural ruby.

Ruby pendant

If you do manage to find a natural, high quality, untreated ruby then snap it up as they are extremely rare!  However you should be warned that you will need deep pockets (far beyond our own means sadly) to keep hold of it!

 

Are diamonds really a girl’s best friend…?

In the next few posts we’re going to take a closer look at diamonds.

Diamond in tweezers

 

Diamonds are notorious for their desirability and associated price tag, they are apparently a girl’s best friend, forever and a long standing essential in engagement rings.  Depending upon where you read the name comes from “Adamas” the ancient Greek word for “unconquerable” but other sources cite the name as meaning “indestructible.”  Either way because of its durability the diamond has been revered as far back as 800 B.C. in India which was the first major source of diamond and it’s easy to see why when you find out that they are the hardest natural substance found on Earth (10 on the mohs scale), impermeable to acids or solvents, with a melting point of an unimaginable (to my mind) 3547’C!

One of the more surprising facts about diamonds to my mind is the fact that whilst our high street and designer jewellers would be bereft without their bevy of brilliant cut beauties, the majority of mined, natural diamonds don’t actually get made into jewellery.

So what makes diamonds so desirable?  Of course, like most gemstones, they are rare, having been made over a billion years ago.  They are expensive to mine, it’s said that to produce one carat of diamond around 250 tons of earth will be mined.   They are expensive to facet, with around 50% of the original weight being lost during preparation.

Uncut diamonds were worn as talismans for protection in battle and to ward off illness, floods, thieves, evil spirits and even snakes, so depending upon your superstitious nature there may be nothing else that will do!

 

Picture from Wikipedia “Diamond”