Traditionally, precious gems are Diamonds, Emeralds, Sapphires and Rubies while other gemstones such as Garnet, Aquamarine, Tourmaline, Peridot Opal are considered semi-precious gems. This distinction is rarely used these days, with fine quality Garnet such as Demantoid, Spessartite and Tsavorite, also Tourmaline,Tanzanite,Spinel,Chrysoberyl along with many others commanding high prices in today’s markets.
The Mohs’ scale of mineral hardness, invented in 1812 by the German mineralogist Friedrich Mohs, is based on ten minerals; from Talc assigned a hardness of 1, to Diamond with hardness of 10. This scale is a ‘relative’ scale and does not measure actual hardness but how easily a stone scratches. The Absolute Hardness Scale is determined under precise, controlled laboratory conditions using an instrument called a sclerometer. Using this scale, Talc still has a hardness of 1 but Diamond has a value of 1,600. This means a Diamond is 1,600 times harder than Talc. By the Mohs’ scale, Sapphires and Rubies have a hardness of 9 and Emeralds between 7.5 and 8. By comparison, the Absolute Hardness of Sapphires and Rubies is 400 and an Emerald is 100.
So, when choosing your stone, give consideration into how it will be used, every day use such as an engagement ring would require harder stones like Sapphire, whereas softer stones such as Tanzanite would be more suitable for occasional use, or set in pendants and earrings, where they are less likely to scratch. Unsure? please feel free to contact us for advise.
Our expert gem-cutters take a long time assessing the rough/badly cut stone before deciding the best way to cut it. They consider things like the size of the finished piece by cutting away as little as possible; using the correct angles to take advantage of the refractive index of the stone to increase brilliance; along the way removing any faults and inclusions and using the correct depth to also maximise colour.
Transparent gems are best cut into a pattern of highly polished flat planes or angled surfaces called facets, each facet acts as a mirror to maximize the way the stone reflects light and determines its brilliance. The more popular cuts are called rounds, marquise, cushion, princess, emerald and pear shapes.
Other types of gemstones that are opaque and do not rely on the way the light hits it for their value or beauty. Agate, Onyx, Turquoise, Opal and Malachite, for example, are best cut round and smooth as cabochons,
In the case of Sapphires and Rubies, very dark and/or semi-transparent/included stones are sometimes cut into cabochons. Any stone showing asterism is referred to as Star Sapphire or Star Ruby. These stones are never completely transparent, because they must have enough silky, needle-like inclusions to produce a star. When orienting asteriated gems, the star must be centred at the apex of the cabochon. Other examples popular cabochons are Chrysoberyl and Alexandrite “Cat’s Eye”
Gem cutting is an exact science and best left to professionals. A well-cut gem in our opinion is far more valuable than a similar stone cut with less forethought. We strive to only produce perfectly cut gems that truly enhance the beauty of a gem.
Gemstone clarity is an important factor when evaluating the value and quality of a stone. Gem dealers and professional jewelers use a Clarity Grading System to assign the clarity of gems. Organizations such as the GIA (Gemmological Institute of America) use charts and grading system to reasonably assess any gemstone on clarity. While there are many types of charts, it should be noted that most minerals will always have inclusions and these inclusions will not necessarily devalue the gemstone, in fact in certain circumstances, inclusions are welcomed and will add value, an example being Russian Demantoid with “horsetail” inclusions.
Although the exact wording may be different from chart to chart, we tend to use the old grading style of:
Clean – no obvious inclusions with a 10x loupe
Eye clean – no visible inclusions at arms length, difficult to see with the naked eye
Included – obvious inclusions, which can still be very beautiful.
PLEASE NOTE: Our stones are hand selected so rarely will a gem fall into this category.
Coloured gemstones are also divided into:
Type I (stones with very little or no inclusions such as aquamarine, topaz, tanzanite and zircon),
Type II (stones that often have a few inclusions such as sapphire, ruby, garnets and spinel),
and Type III (stones that usually always have inclusions such as sphene, rubellite, emeralds).
Gemstones are weighed in carats (1 carat = .2 of a gram or 1 gram = 5ct) and in points (1 point = 0.01 carat). Gemstones are usually traded in $ per carat. The larger the stone the more rare it is, so the price per carat often increases with the size.
For example a fine quality blue Sapphire of 1ct might be priced at $1000 per ct , whereas a 3ct gem of the same quality could be $3000 per ct, generally as the size increases so does the price per ct.
Gemstones can be found in every colour of the rainbow; from red ‘pigeon blood’ rubies, orange garnets, yellow citrine, green emeralds, turquoise, purple amethyst and blue sapphires. Many individual gemstones come in a variety of colours. Sapphires are known in every shade of blue from very pale sky blue to almost black, but they can also be found in green, yellow and even purple. Sapphires and rubies are both made of the mineral corundum and a point of contention is when such a stone is a very light tone of red or pinkish red. Some people call it a ruby while others call it a pink sapphire, insisting that a very intense red colour is necessary to justify the use of the term ruby. Nowadays laboratories tend to classify anything that is orange red or pinkish red as a Ruby.
Colour has a large bearing on the price of a gemstone, generally depending on the rarity of the colour for that particular stone, the intenseness and clarity of the colour and the popularity of the colour among buyers.
Here we select a piece of rough as close as possible to the shape of the particular shape and size of the clients order. This piece weighs 38.35ct before any work as started.
The Amethyst is ground into a shape close to the particular design desired, then glued/waxed to a brass dop ready to start the cutting process.
The dopped material is then placed into the faceting machine and grind down at different angles to give you the facets. Various lap grit sizes are used, getting finer and finer until the stone is polished and your left with a finished pavilion.
The stone is then removed from the machine still attached to the brass dop and placed within the transfer block. The stone will be transferred to the female dop exposing the side in which the crown will be cut.
The same process as the pavilion is then repeated until you eventually have a finished polished piece. The stone is removed from the dop and cleaned with alcohol and warm water.
16.88ct Clean Bolivian Purple Amethyst