7 FACTS ABOUT GEMSTONE CUTTING YOU DIDN’T KNOW AND THE PROCESS OF GEM CUTTING

7 FACTS ABOUT GEMSTONE CUTTING YOU DIDN’T KNOW AND THE PROCESS OF GEM CUTTING

Posted by Sasha Gammampila on 1st Aug 2016

Well, this is something I have been meaning to blog about for a while and I think it is about time that I get around to it! 

 

Following is how our natural sapphires are processed.

 

STEP 1 - ROUGH SAPPHIRE

 

Rough gemstones come in all different shapes.

 

Depending on which geological environment they are found in, the shape of the rough gemstone can change significantly; they could be mined in river or they could be mined underground.

 

Crystallographically sapphires are formed in bi-pyramidal form. If the gemstone was mined in the river bed it is likely to be in an appearance of a pebble as you would expect. If they were mined underground then it is likely to have more broken, sharp edges.

 

Natural gemstones are faced with many environmental changes and as such they are unlikely to be completely clear. We have to expect some imperfections within the stone; that is what prove the gemstone is natural. We inspect the rough gemstone for colour and any imperfections of the stone. This we do by immersing the rough sapphire in water or with a bit of oil rubbed on the gem.

 

FACT 1: 95% of the mine's cost is covered by 5% of its production.

 

Hence why the finer quality gemstones attracts a higher price.

 

Unlike other colours, yellow sapphires are coloured by a few different methods. One of them being colour centres. Some colour centres react in light and minor heat and loose its colour. When selecting yellow sapphires, we leave the rough yellow sapphire in sunlight for a couple of days to ensure that it does not loose its colour.

 

Exportation of rough gemstones from Sri Lanka is prohibited. All gemstones must be cut before they are exported. This is to protect the locals in the industry as until the gemstone is cut it is difficult to determine its value.

 

Family, (my father to be specific) residing in Sri Lanka has given me an incomparable opportunity to access these magnificent gemstones first hand. I am beyond proud to present our magnificent jewels to my clients.

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STEP 2 - PREFORMING THE ROUGH STONE

 

Natural sapphires are coloured by colour patches or colour banding. Majority are not completely coloured throughout the crystal. Therefore the gem cutter has to ensure the colour patch is placed suitably to reflect expected colour throughout the sapphire once we finish cutting and polishing.

 

Colour patch can either be placed near the culet or it could also be placed near the girdle. This will ensure the gemstone appears in the desired colour by internal reflection of light.

 

We also have to attempt to place inclusions along the girdle line as this is where it will be least visible. Working around colour and inclusions is constantly challenging.

 

As a knowledgeable cutter, my father is heavily involved in this process, inspecting all our rough gemstones.

 

FACT 2: The widest point of the circumference of a gemstone is called the ‘girdle’.

 

FACT 3: The part of the gemstone below the girdle is called the ‘pavillion’.

 

FACT 4: The part of the gemstone above the girdle is called the ‘crown’.

 

At this point we will decide what shape and cut the gem should be cut in. Shape and cut depends on the shape of the rough gemstone, inclusions and the colour patches. As the rough sapphires are naturally grown in an elongated shape unlike cubic shaped rough diamonds, you will rarely come across a round sapphire.

 

Appropriate cutting angles should also be placed in the pavilion in order to achieve total internal reflection. This means avoiding windowing and extinctions. Diamonds for example have an angle of 36 degrees whereas sapphire must be cut at least at 39 degrees. This means sapphire is a deeper cut stone than a diamond.

 

After carefully inspecting the rough gemstone, the cutter will then proceed to pre-from the stone. During this process the cutter will also remove any inclusions that affect the durability of the stone. They also naturally break off during the cutting process.

 

Following natural sapphire was preformed from a 6 carat rough stone. Once preformed it weighed 3.5 carat. 

 

 

STEP 3 - FACET AND POLISH THE STONE

 

Coloured gemstones including sapphires are cut for colour, second comes the brilliance.

 

FACT 5 - There are two types of facets.

 

  • brilliant facets (triangle shaped) - designed to maximise light reflected from within the stone back to the eye.
  • step facets (rectangular shaped) - designed to maximise the appearance of the colour by retaining reflection of light within the stone.

 

FACT 6 - It is the cutting angle of the pavilion that makes your gemstone sparkle by reflecting light back to the eye. Ideal cutting angle of the pavilion differs from gem to gem.

 

FACT 7 - Expected yield of a well cut sapphire is 25%-30% of the weight of its rough.

 

Step facets are usually used on the pavilion of oval and cushion shapes to maximise the appearance of colour. Brilliant facets are placed on the crown to maximise the brilliance and sparkle. Emerald shape is completely step cut.

 

It is wasteful to use brilliant facets on oval, cushion and round shapes and therefore increases per carat price. Brilliant cut facets also reduces the saturation of colour and is best used in light colour stones to increase sparkle. However if the stone is very dark, we will put brilliant cut facets on the pavilion. This will increase liveliness of a gem which otherwise would have been dull in appearance.

 

Brilliant facets however in radiant and scissor cuts serves the purpose of brilliance and colour. This is because the facets are placed in a few layers.

    

Polishing of the stone needs great care with some cutters specialising in polishing alone. It is done on a copper plate using finest diamond dust. If the dust is not fine enough it will leave polish marks.

 

Until the stone is finished polishing, it is hard to tell the full personality of the gemstone.

 

We have tremendous respect and appreciation for all natural gemstones irrespective of their quality. Each and every natural gemstone has a story and a place where it belongs. 

 

Following is once the above preformed sapphire was cut ad polished. It now weighs just over 2.2 carat.

 

 

Shop our magnificent sapphires online or email  sasha@deliqagems.com with your enquiry.