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Jewellery - Whitby Jet and Blue John glossary of terms.

Glossary of Jewellery terms


Amber – Along with Whitby Jet, Pearls and Coral, Amber is an organic gemstone, which originates from the fossilized resin excreted from pre-historic pine trees which flourished more that 30 million years ago. The word ‘electricity’ comes from the Greek name for Amber, ‘electron’, because, when rubbed, amber produces a static electric charge.

The natural beauty of Amber has made it a highly prized gemstone for thousands of years; the Romans especially produced a lot of amber jewellery.

Most Amber ranges from golden yellow to golden orange, but colours from green to black are also found, it may also contain insects, moss, lichen and pine needles,  its unusual markings and warm, vibrant colours have continually captivated its wearers so that even today, amber jewellery is a coveted gemstone, escalating in popularity.  

It is a soft, warm stone with a hardness of 2.5 on the Mohs Scale.

Ammonite – Fossil Ammonites are around 150 million years old. They can be set to make fascinating and unusual jewellery. The fossilised coiled ammonite shells are found in Dorset and Somerset (light coloured) and North Yorkshire (Dark Coloured).

Baguette Cut – A gemstone cut so that the table is in the shape of a long, narrow rectangle, bordered by four facets each step cut.

|Bar Brooch – A type of brooch in the form of a horizontal bar, often with decoration along its length or set with gemstones at its centre.

Bezel – The top metal rim or setting edge that surrounds the cavity which holds a gemstone.

Blue John - Blue John is one of England’s most rare and beautiful gemstones. It is a member of the fluorite family and is well known for its distinctive bandings of colour with traces of golden yellow iron stain.

Blue John can only be found in one hill, about three quarters of a mile west of the small town of Castleton in Derbyshire. Different parts of the hill are characterised by different patterns of colour banding in the Blue John, these are known as ‘veins’ and there are at least 14 different veins of Blue John available.

Blue John was created 290 million years ago after remote volcanic activity forced a mixture of minerals and very hot water into gaps and faults hidden deep within ancient limestone rock. When this chemical mixture began to cool, it would crystallise out into the gaps and form into the gemstone.   

The industry of working Blue John started in the 17th century after an unknown person discovered how to treat the stone with resin so that it could be cut and polished and used for ornamentation. The heyday of the industry lasted from around 1760 to 1860, when fantastically elaborate clocks, vases, candelabra and cassolets (perfume jars) were made to decorate Britain’s stately homes and furnish the houses of aristocracy.  The core of these ornaments would be made from Blue John and then surrounded with the most skilfully crafted ormolu finishing’s. There were about 20-30 firms working with the gem at this time with the most famous and celebrated of the manufacturers being Matthew Boulton, who was prominent amongst the leaders of the industrial revolution.

Nowadays, there is not nearly enough Blue John left to make large decorative pieces with, and the industry is limited to the manufacturing of fine pieces of jewellery instead. At the forefront of this specialised craft is C.W. Sellors, a Derbyshire based jewellers who’s passion for this local gemstone was what started this established company over 35 years ago. C.W. Sellors has now even patented the backing of Blue John with Mother of Pearl, to provide extra stability as well as adding an iridescent look to the stone. C.W. Sellors’ Blue John set jewellery can be found in a wide range of designs, from classic pieces set in sterling silver to high end one off items set in precious metals, and accented with sparkling diamonds.

Blue John has a hardness of 4 on the Moh’s Scale.

Brilliant Cut – The style of cutting a gemstone, usually a diamond, with many facets of different shapes and sizes so as to increase its brilliance by minimizing the amount of light that escapes at the bottom of the stone. It consists of 32 facets above the girdle and 24 below. 

Cabochon – A stone cut with a domed, smooth, rounded surface, with no facets and highly polished.

Carat – The unit of weight for a diamond or other gemstone. There are 100 points to every 1 carat.

Channel Setting – A style of setting to secure a row of identically sized and shaped stones, whereby the stones sit within two parallel walls of metal which are then pushed together to hold the stones in place.

Claw Setting – A style of setting a gemstone in which the stone is held above the girdle by a series of encircling, vertically projecting prongs (claws) which are pushed over the stone, securing it in place.

Crown – The upper part of a cut gemstone. The part of a brilliant cut above the girdle, which usually protrudes above the setting.

Cushion Cut – A style of cutting a gemstone with a square or rectangular shape but having rounded corners.

Culet – The point at the base of a brilliant cut diamond. These appear as a small flat facet on old-cut diamonds.

Cut – The final form into which a rough gemstone is shaped.

Emerald Cut – The style of cutting a gemstone, usually a diamond or emerald, so that the shape or table of the stone are square or rectangular, with chamfered corners and the sides are step cut.

Facets – One of the small, flat surfaces of a cut gemstone. Facets are of various shapes and sizes, and the many arrangements of the facets depend on the style of cut.

Gold – The most malleable and ductile of all metals, it is unalterable by heat and moisture, and will never tarnish. Pure gold is too soft for practical use alone and so is alloyed, the purity expressed in carats:

9ct – Is 37.5% or 375 parts out of 1000 pure 24ct gold.

18ct – Is 75% or 750 parts out of 1000 pure 24ct gold.

Alloys of silver, copper and zinc are then added in different quantities for hardness and durability.

(White) Gold – An alloy of gold with a high percentage of other white metals to make it a pale gold colour. It is then plated with rhodium for a bright white finish.

Girdle – The thin band that forms the widest circumference of a brilliant cut stone and that separates the crown above it from the pavilion below.

Hallmark – The mark(s) stamped on some items of gold or silver that attests the purity of the metal, in compliance with legally established standards. The marks also include a date letter, as well as a maker’s mark and an assay mark to indicate the office that does the assaying.

Lap Setting – A gemstone which is set down into the bezel, with the top of the stone protruding upwards, to be cut back down into a domed shape which sits flush with the top of the bezel.

Marcasite – These are small cut and faceted stones made from an iron ore called Hematite. They are a dark grey, metallic colour, usually seen in conjunction with other stones; as a cluster, for example, to give added sparkle.

Marquise Cut – A gemstone that is cut into a boat shape with points at the top and bottom.

Moh’s Scale - The Moh’s scale of hardness is the most common method used to rank gemstones and minerals according to their hardness, 1 being the softest and 10 being the hardest.  It was devised by German mineralogist Friedrich Moh in 1812. See table below.

Mother of Pearl – White, grey and pink Mother of Pearl are all types of shell. The white shells come from Australia, the grey from Indonesia and New Zealand, and the pink is actually mussel shell from the Mississippi River in USA. All shells are fairly soft and lustrous, whith a hardness of 2.5 on the Mohs Scale.

Pavé Setting – Literally, paving-stone setting. A style of setting in which many small gemstones are set very close together in a mass so as to cover the entire piece and to conceal the metal.

Pavilion – The part of a brilliant cut stone, below the girdle.

Pear/Teardrop Cut – A style of cutting a gemstone into the shape of its name, with a point at the top, tapering out into a rounded bottom.

Plating – A coating of precious metal over another metal base. See also vermeil.

Platinum – The most valuable and rare of all the white metals. It is very heavy and does not tarnish.

Point – A unit of weight for a diamond or other gemstone. There are 100 points to every 1 carat.

Rub-Over Setting – A style of setting a gemstone whereby metal is pushed over the girdle of the stone to secure it in place.

Seed Pearl – A very small, round pearl, natural or cultured.

Setting -  1.) The method in which a stone or stones are secured in a ring, pendant, brooch etc.

  1.  )Channel Setting, Claw Setting, Rub-over Setting, Pavé Setting, Cluster Setting, Lap Setting.

Step Cut – A style of cutting a gemstone so that, below the table, there are a number of sloping, parallel rows of four sided facets that increase in size as they approach the girdle and then decrease as they descend to the culet, thus giving the impression of steps.

Sterling Silver – An alloy of silver, that when used for jewellery in the UK has a fineness of 0.925 parts silver and 0.075 copper.

Vermeil – Gilded silver, i.e. sterling silver covered with a layer of gold by plating.

Whitby Jet – Whitby Jet is an organic gemstone made from the fossilised wood of the ancient monkey puzzle tree (Araucaria). Although deposits of Jet have been found in many places around the world, such as North America, Spain, and the Baltic regions, the Jet found around the North Yorkshire coast around Whitby has always been considered the finest due to its stable nature and the mirror like shine it can achieve when being polished. This is due to the lack of oxygen and immense pressure compacted onto the material during the fossilisation process.

Jet is one of the oldest gemstones known to man, with pieces of worked Jet dating back to the stone age, It was also highly prized during the Bronze age, and a large Jet industry existed during Roman times, the principle manufacturing taking place in a workshop in the city of York, which distributed items of worked Jet to all corners of the Roman Empire.

However it was during the Victorian era when Whitby Jet reached its height of popularity. Worn by Queen Victoria after the death of her husband Prince Albert, the local gemstone became an overnight sensation.

Because of its royal patronage, its ability to be carved into the most intricate of designs, its comfortability when being worn due to its lightness in weight, and also its world famous mirror-like shine, Victorian society could not get enough of this local product.

One hundred years on, Whitby Jet is now enjoying a well earned renaissance. With its associations with mourning long gone, this ever more rare local gemstone is now set in exciting modern designs using traditional hand crafting skills as well as revolutionary new techniques including Computer Aided Design (CAD).

Whitby Jet is now more likely to be found set in high end jewellery, alongside diamonds and in 18ct gold and platinum.

Whitby Jet has a hardness of 2.5 on the Moh’s Scale.


Moh’s Scale of Hardness

Named for German mineralogist Friedrich Mohs (1773-1839), the Mohs scale is widely used as a hardness standard for gems and minerals. The concept is simple, employing what is often called the “scratch test.” Once Mohs determined that diamonds were the hardest of all materials, he assigned it his highest possible number, Mohs 10. He then sought the softest mineral he could measure, talc, and gave it the number 1. To establish a relative rating for all the common gems and minerals, Mohs rubbed hundreds of materials together. The one that scratched the other received a higher number on his scale. Knowing this concept prepares you to keep your harder gemstones from scratching softer gems and jewellery metals.  


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