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What is Gold?

Extract from the book, 'All About Gold' by Michael Moore. Publisher, Technical Author Services Pty Ltd


Gold is a malleable and ductile metal. Just a single gram can be beaten into a sheet of metal one square meter. An ounce of gold will cover 300 square feet. This is how gold leaf is produced. Gold leaf can be beaten so thin it becomes translucent so you can almost see through it and the light you see through it appears greenish blue, since gold reflects yellow and red. Gold will readily form an alloy with many other metals. These alloys are then used to increase the hardness of the gold or to create various colors. Native gold contains usually eight to ten percent silver, sometimes more - gold alloys with silver content over 20% are called electrum. As the amount of silver increases, the color becomes whiter and the specific gravity becomes lower.

Gold is an excellent conductor of heat and electricity making it ideal for electrical components and contacts. Is not affected by air or most reagents (A substance used in a chemical reaction to detect, measure, examine, or produce other substances.). Heat, moisture, oxygen, and most corrosive agents have virtually no chemical effect on gold, making it an excellent metal for use in coins and jewelry; conversely, halogens (Any of a group of five nonmetallic elements with similar properties. The halogens are fluorine, chlorine, bromine, iodine, and astatine. Because they are missing an electron from their outermost shell, they react readily with most metals, including gold, to form salts) will chemically alter gold, and aqua regia (A corrosive, fuming, volatile mixture of hydrochloric and nitric acids, used for testing metals and dissolving platinum and gold. Also called nitrohydrochloric acid) dissolves it as well.

You can eat it too! Generally gold is considered not harmful if consumed in very minute quantities and is sometimes used as a food decoration in the form of gold leaf. Gold flake and gold duct, for example, was used in Medieval Europe by the nobility to decorate their food and drinks. Gold has the E Number 175 and is still used in Goldwasser (German: "Goldwater"), a traditional herbal liqueur produced in Gdansk, Poland and Schwabach, Germany.. There are also some expensive $1000 dollar cocktails containing flakes of gold leaf. However, consumption and accumulation of large amounts of gold or gold compounds, in the body can still be toxic and the symptoms are similar to those of heavy metal poisoning. Pure metallic gold is tasteless by the way. Much better to look at it than eat it.

Gold is a yellow soft malleable metal considered valuable, both as an investment and as an adornment.

Chemically, gold does not react with most chemicals, but is affected by chlorine, fluorine, aqua regia and cyanide. Gold dissolves in mercury, forming amalgam alloys, but does not react with it. Gold is insoluble in nitric acid, which will dissolve silver and base metals, and this is the basis of the gold refining technique known as "inquartation and parting". Nitric acid has long been used to confirm the presence of gold in items, and is the origin of the colloquial term "acid test," referring to a gold standard test for genuine value.

Here are some technical specification about gold

Name: gold
Symbol: Au
Number: 79
Chemical series: transition metals
Group: 11
Period: 6
Block: d
Appearance: metallic yellow
Standard atomic weight: 196.966569(4) ?g.mol-1
Electron configuration: [Xe] 4f14 5d10 6s1
Electrons per shell: 2, 8, 18, 32, 18, 1
Physical properties
Phase: solid
Density (near r.t.): 19.3 ?g.cm-3
Liquid density at m.p.: 17.31 ?g.cm-3
Melting point: 1337.33K (1064.18C, 1947.52F)
Boiling point: 3129K (2856C, 5173F)
Heat of fusion: 12.55 kJ.mol-1
Heat of vaporization: 324 kJ.mol-1
Heat capacity: (25C) 25.418 J.mol-1.K-1
Vapor pressure
Atomic properties
Crystal structure: cubic face centered
Oxidation states: -1, 1, 2, 3, 4, 5, 6, 7 (amphoteric oxide)
Electronegativity: 2.54 (scale Pauling)
Ionization energies: 1st: 890.1 kJ/mol 2nd: 1980 kJ/mol
Atomic radius: 135 pm
Atomic radius (calc.): 174 pm
Covalent radius: 144 pmv
Van der Waals radius: 166 pm


Magnetic ordering: no data
Electrical resistivity: (20C) 22.14 nO.m
Thermal conductivity: (300K) 318 ?W.m-1.K-1
Thermal expansion: (25C) 14.2 ùm.m-1.K-1
Speed of sound (thin rod): (r.t.) (hard-drawn) 2030 ?m.s-1
Young's modulus: 78 GPa
P(Pa) 1 10 100 1 k 10 k 100 k
at T(K) 1646 1814 2021 2281 2620 3078
Shear modulus : 27 GPa
Bulk modulus: 220 GPa
Poisson ratio: 0.44
Mohs hardness: 2.5
Vickers hardness: 216 MPa
Brinell hardness: 2450 MPa
CAS registry number: 7440-57-5

Applications of Gold
Gold has many applications in a variety of uses and industries.

Commonly known to most people of course is gold bullion in the form of coins and gold bars and jewelry. Gold has been used as a currency for hundreds of years. Gold is also used extensively in industrial applications, dentistry, food and the health industry.

How it is used tends to determine the karat or amount of gold in proportion to other metals. The higher the karat the purer the gold. Gold is usually alloyed with other metals to increase its hardness and durability and the amount of hardness required determines the use to which the gold is used.

Medium of Exchange
Gold has been used throughout the centuries as a medium of exchange. Typically in the form of coins and small bars. As gold is a soft metal and easily wears down, gold intended for circulation was usually alloyed with copper and other base metals to give it some hardness and durability. Much as is done in modern times with gold jewelry. The gold content of gold alloys is measured in karats with 24 karats being pure gold, 22 karats being 22 parts of gold to 2 parts other metals and so forth.

The composition of alloys used in Jewelery in many countries is denoted in the 'carat system' (spelt Karat in the USA and on the continent). Also for hallmarking purposes gold is expressed in parts per thousand. Hence 999 and 990 parts per thousand (the other parts being another metal or combination of metals such as silver or copper for example). Here is a list of the karats and proportions of gold to alloys:

22 karat is 916.6 fine
18 karat is 750 fine
14 karat is 585 fine
9 karat is 375 fine

In the USA this is another way of looking at it.

% of Gold
24 100 1000
22 90 900
18 75 750
15 62.5 625
14 58.33 583
10 41.67 417
9 37.5 375
8 33.3 333

24 karat is pure gold with nothing added. This is the purest gold available. Also has a fineness of 1000, but this is expressed as 999 being 999 parts per 1000. This is because it is very difficult to get real pure gold with absolutely no impurities whatsoever and possibly for legal reasons as well. This applies to gold coins a lot. Canadian Gold Maples, for example are listed as 99.999% pure gold.

gold bullion

There are other hallmark standards available as well as the above but these are the most common. This tells you how much gold there is in a gold piece. 14 karat, for example, is 585 parts gold to 415 parts other metal. The alloys used varies with the purpose to which the gold is put. For jewelery and dental work usually the combination is gold, silver and copper. Sometimes with the addition of zinc or nickel. For dental alloys, palladium and platinum are usually added as they are particularly stronger and hard wearing. Nickel is not much used these days as some people have allergic reactions to it and it is now illegal in some European countries. 18 karat gold is more popular for gold jewelery with a 75 percent gold and 25 percent other metals ratio, usually silver or copper or a mixture of both.

The 14 karat standard is used more extensively in industry and for such things as pen nibs, circuit boards etc. It is also used in such jewelery as bracelets where more durability is required due to more use.

There is also a 10 karat, containing 41.7 percent gold and known therefore as 417. This is really just a cheaper version of the 14 karat and used for cheaper jewelery. If you are buying gold jewelery you should check the karat of the piece as it may be actually 10 karat and not 14. Becoming more popular these days is the 9 karat with 37.50 percent gold and 62.5 percent other metals.

Antique and early Russian jewelry will often be found to be 18 karat gold containing 25% copper. It has a distinct copper cast, which creates an attractive warm color known as rose gold. Fourteen karat gold-copper alloy is almost identical in color to certain bronze alloys, and both may be used to produce police and other badges interestingly. Blue gold is made by alloying with iron and purple gold made by alloying with aluminum, although this is extremely rare.

Green gold is made by alloying gold with pure silver alone. White gold alloys, very popular these days with rings and bracelets, are made with palladium or nickel. White 18 karat gold contains 17.3% nickel, 5.5% zinc and 2.2% copper is silver in appearance. Since nickel is toxic, however, you will not find it in any European white gold due to legislation in Europe. White gold alloys are available based on palladium, silver and other white metals however, although the palladium alloys are more expensive than those using nickel. High-carat white gold alloys are far more resistant to corrosion than are either pure silver or sterling silver. An example of using color contrasts between laminated colored gold alloys to produce decorative wood-grain effects can be found in the Japanese craft of Mokume-gane.

Medical Uses
Recorded examples of gold used in dentistry go back as far as the Etruscans in the seventh century BC but probably unrecorded may go back a lot further. The Etruscans used gold wire to hold in place substitute animal teeth when their own were damaged or needed replacing. The first book to mention using gold in dentistry was 1530 in Leipzig in which gold leaf was recommended as filling for cavities. Gold has been recommended in dentistry due to it being easy to work with and being resistant to corrosion. In addition it is non toxic, or in other words biocompatible, and can be attached to the body even in the mouth. Gold alloys are used in restoration work as gold malleability makes it easy to produce molars, crowns, incisors and permanent bridges.

Gold was seen to be beneficial to health even in medieval times and modern day medicine uses gold salts as an anti inflammatory agent in the treatment of arthritis. Salts and Radio isotopes of gold are also currently used in pharmacology.

Industrial Use
Gold has extensive use in industry both in manufacture as well as component parts.

Gold has achieved widespread use in the electronics industry with the advent of computers as an ideal metal for connectors due to its resistance to corrosion, its excellent electrical conductivity and reliability. Gold is used in Audio and Video connectors, USBs, sliding and switch contacts as well as certain computer equipment, aircraft and spacecraft components.

Gold can be drawn into a very fine thread and used in embroidery as well as jewelry and gold solder is used for joining gold components of jewelry. The gold solder used must, however, he of the same carat as the gold being joined if the piece is to be of Hallmark* quality. Gold solder is made with three different melting points, easy, medium and hard. Using a combination of these goldsmiths, people who fabricate gold such as gold jewelry, can solder complex varying gold karat pieces together.

Gold is also used in photography. Gold toners are used to shift the color of silver bromide black and white prints to the brown and blue tones to give that old fashioned photo look. Eastman-Kodak published formulae for several different types of gold toners at one point for this purpose. This was to prevent deteriorisation due to oxidation of the silver image which can deteriorate over time.

Gold is used in electrical wiring also. Although silver is a better conductor, gold is more resistant to corrosion. For this reason gold electrical wires were used during the Manhattan Project's** atomic experiments. Colloidal gold is gold nano particles suspended in water. These particles are a sub-micrometre-sized particles of gold a few nm (nanometre, one millionth of a millimeter) across. They can be in various shapes such as rods spheres and cubes, for example, and have a variety of uses including as a therapy for rheumatoid arthritis, as well as a holder for specific antibodies to be used as probes for the presence and position of antigens*** on the surfaces of cells (Faulk and Taylor 1979).

Moving back in history again, Colloidal gold was used by the Romans to colour glass various shades of yellow, red, or mauve, depending on the concentration of gold. Colloidal gold has been also used in the 16th and 17th century up to Michael Faraday who called colloidal gold, "activated gold". He was among the first to recognize that the color was due to the minute sized particles.

Gold, and alloys of gold, are also used as a conductive coating to biological specimens and on other nonconducting materials such as plastics and glass to be viewed in a scanning electron microscope. The coating has a triple purpose in this application. Gold's high electrical conductivity drains electrical charge to earth, and its high density slows the electrons in the SEM's electron beam, contributing to the depth which the electronic beam penetrates. This improves the definition of the position and topography of the specimen surface and increases the spatial resolution of the image making it easier to see and understand the depth of the specimen. Gold also produces a high output of secondary electrons when irradiated by an electron beam, and these lowenergy electrons are the most commonly-used signal source used in the scanning electron microscope.

Gold is the favored metal for medals of honor such as the Olympics, Nobel and many other medals of honor. It is the favored metal for coins and this book covers some of the various types of gold coins that have been and continue to be used through the ages.

Gold is used as the protective coatings on many artificial satellites and in infrared protective faceplates in thermal protection suits and astronauts' helmets due to being an excellent reflector of infrared as well as visible light. Some high-end CDs use gold as the reflective layer.

Gold has many other uses including cancer research and treatment, as well as in automobiles.

More information on buying gold can be obtained from Gold Price.

Hallmarks were originally adopted in England in the 14th Century as an official mark to designate the finesse and genuiness of precious metal. Also often to indicate the maker and sometimes the date of manufacture. Hallmarks are stamped or punched on the metal and are a good indicator of the quality of the item.


**Manhattan Project:
The project to develop the first nuclear weapon (atomic bomb) during World War II by the United States, United Kingdom, and Canada. Previously called the Manhattan Engineer District (MED), it refers specifically to the period from 1941 to 1946 under the control of the U.S. Army Corps of Engineers, under the administration of General Leslie R. Groves.
Reference: Manhattan Project

*** Antigen:
An antigen(from antibody-generating) or immunogen[citation needed] is a substance that prompts the generation of antibodies and can cause an immune response.[1] The word originated from the notion that they can stimulate antibody generation. We now know that the immune system does not consist of only antibodies. The modern definition encompasses all substances that can be recognized by the adaptive immune system. In the strict sense, immunogens are those substances that elicit a response from the immune system, whereas antigens are defined as substances that bind to specific antibodies. Not all antigens produce an immunogenic response, but all immunogens are antigens (Immunobiology, Janeway and Travers, 1994

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