Diamonds 

What are diamonds

Diamonds are one of the world’s most important mineral resources, formed from pure natural carbon with the atoms organised in a close-packed cubic arrangement that gives them their hardness.
They are the hardest of all gemstones and the hardest transparent substance known to man. They are formed by extremely high pressure and temperature and found in 'Kimberlite' or 'Lamproite' pipes produced by volcanic magma, millions of years ago.
Because of their hardness they make ideal Gemstones, and also have many industrial uses.
A rough diamond resembles a common pebble, but properly cut and polished, they come to life with their 'fire' or brilliance. The magnificent optic properties are caused firstly by their high refractive index (2.417 if you really want to know), or light bending ability, this allows it to throw back almost all of the light which enters it, giving it's lustre.
Secondly, it exhibits very high dispersion (0.058), which is the ability to separate the various colours of the spectrum thus giving it the 'fire' for which it is famous.

Gemstones

Fewer than 20% of the diamonds mined each year are suitable for use as Gemstones.
Four factors are used to determine quality:

• Carat Weight
• Cut
• Clarity
• Colour
  

Carat Weight

One Carat = 0.2grams, one Carat is also = 100 points, so a 50 point diamond is described as 0.50 Carats.

Cut

How well the diamond has been cut? The cut of the diamond gives it a unique sparkle or brilliance by allowing the maximum amount of light to enter and be reflected back. There are six different shapes to which a diamond is cut, round brilliant cut diamonds account for more than 75% of all diamonds sold, the other cuts are marquise, pear shaped, emerald-cut, oval and heart shaped.

Clarity

Defined by how flawless the diamond is. Flaws consist of natural phenomena known as inclusions such as scratches, impurities, cracks and non-crystallised carbon.
The following shows the standard grading used for clarity:

• Flawless (F) - No inclusions or blemishes seen under 10X magnification.
• Very, Very Slightly Included (VVS1/VVS2) - minute inclusions that are difficult to see under 10X magnification.
• Very Slightly Included (VS1/VS2) - Inclusions are clearly seen but minor and small.
• Slightly Included (SI1/SI2) - Inclusions are noticeable and fairly easy to see under 10X magnification but not noticeable to the unaided eye.
• Imperfect (I1/I2/I3) - Inclusions that are obvious under 10X magnification or can be seen with the naked eye.
  

Colour

Grading standards for colour range from D to Z as shown below, with Grades of D to H being preferred for fine jewellery. The value of the diamond decreases as you progress down the scale:

The market value of a diamond is a combination of these four factors with hundreds of possible combinations, the current trend is to give high priority to colour, then clarity, then cut and finally to carat weight.

Gold

Coloured Gold Alloys

Every collector has at some time come across an item made of gold but of a different colour than pure gold, or an article produced from a combination of coloured gold alloys.   Old masters of sophisticated shades of coloured gold, particularly in jewellery, were able to produce many interesting effects.   Below is a short description of the best known colour shades:

Red gold – its colour is the best known and the oldest of the colour shades.   The red is obtained by adding copper to the alloy.   From early times red gold was very valuable.   Even earlier, before the methods for determining the purity of gold alloys became universally known, the quality of an alloy was judged according to its red colour.   Red gold is usually made from a purity 750/1000 or less; the main difficulty is not attaining the desired colour but the proper hardness of the alloy.

Green Gold – an alloy of gold with silver or cadmium.   The shade of green is determined by the amount of silver in the alloy.

Blue Gold – an alloy of gold and steel, usually in a proportion of 18:16; gold of this shade most wide spread in Europe.   Perhaps because steel jewellery was popular in the 19th century.

White Gold – an alloy of gold and metal, which intensively decolours it so that the alloy is a pure white colour; it is absolutely unchangeable in the air can be polished to a high lustre.   Nickel and palladium decolour the most intensively.   Less often rhodium, platinum, copper and zinc are added to the alloy of white gold.   White-gold alloys were known at the beginning of the 20th century, but they did not find favour with goldsmiths at first.   They were used more because of their hardness in the watch making industry – for the gearing and watch spring alloys.   Further research led to suitable alloys even for jewellery making, where they won favour as a successful substitute for expensive platinum.   In general, white gold with the addition of palladium is used for more expensive work, particularly in setting diamonds and similar stones; alloys with nickel are used to produce more commonplace jewellery.

Purple Gold – an alloy of gold and aluminium usually in a proportion of 18:6.   Its colour cannot be called pure purple; it looks more like bronze with a touch of plum-blue.   Purple gold was first shown publicly in 1937.

Gold acquires colour through the addition of various metals to the alloy.   The kind and amount of colour the goldsmith uses in making alloys depends on several factors.   These are the main considerations:

1. An alloy must correspond to legal regulations of purity of an alloy.   In other words, the established proportion of precious to base metals must be retained in the alloy.
2. An alloy must retain all the suitable technical qualities of precious metals so that it can be processed further.   It cannot be either too brittle or too hard; it must not show any defects in casting, hammering, rolling, and pressing, ect.
3. An alloy must have the desired shade of a colour so that the goldsmith can use it for his particular designs, or so that it suits current fashions.It is evident that the goldsmith is restricted in producing coloured alloys and there are a large number of regulations and instructions on the production of coloured alloys of various purities.   For the sake of illustration, we present a short table of the composition of multicoloured alloys of gold (according to K. Taubl); the composition of the alloy is given in thousandths.