Gold history and chemical characteristics :

Gold chemical symbol Au – atomic number 79 – specific weight 19.3; found in nature in the form of specks and nuggets, very often alloyed with other metals. Known since antiquity, used and appreciated by man since prehistoric times, and almost certainly, gold was the first metal ever used by human beings to make ornaments, jewellery, ritual objects and symbols, most likely used before copper.

Then over the centuries for the exchange of goods, to the minting of coins and as a counter value for currency issues by states.

Gold over time has become a symbol of value, purity and loyalty, but also of pomp and wealth, and is used to make jewellery and ornaments.

It belongs to the group of ‘noble metals’, and are those metals that have the following chemical and physical characteristics:

1) They do not oxidise in air or water

2) They are unalterable over time

3) They do not easily combine with other substances

4) They resist acids well.

In chemistry, the metals that are considered noble are: gold, silver, platinum, palladium, ruthenium, rhodium, osmium, iridium.

It is a yellow metal in nature, its melting temperature is 1063°C, and it can take on different colours depending on the metals with which it is combined in the numerous executable alloys usually called: yellow, white, red, pink, green gold.

It is the most ductile and malleable metal of all; one gram of gold can be rolled or wrought to make a sheet with an area of one square metre (thickness of 1/10,000 mm), and one gram of drawn gold can also be used to make one kilometre of wire.

In its pure state it is soft, and to obtain greater mechanical resistance it is alloyed with other metals to obtain specific workability and aesthetic characteristics depending on the use and the object to be made.

It can be alloyed with copper, silver, iron, aluminium, platinum, nickel and many others. The most commonly used colours in jewellery and goldsmithing are yellow, white, pink and red.

Gold is neither altered nor oxidised in the air with oxygen, humidity, heat, caustic acids and alkalis, conversely it reacts with the cyanide ion, and in practice is only affected with aqua regia

(3 parts hydrochloric acid + 1 part nitric acid, CAUTION the preparation of chemicals requires a thorough knowledge of chemistry).

When placed in contact with mercury, it dissolves to form an amalgam. Its remarkable chemical inertness has always made it the material par excellence for the minting of coins and medals and for the production of jewellery and ornaments.

Gold What is the title and what is the carat (kt)

The preparation of a gold alloy must respect the legal parameters with the title*, which is quantified in carats or thousandths, i.e. different units of measurement that indicate the same quantities of pure metal, so 750/000 (thousandths) and 18kt (carats) are the same thing.

The carat (kt) in the case of gold alloys, takes on a different value from the unit of measurement used for the weight of gems and pearls, and acquires the meaning of “purity” by quantifying the parts of gold contained in an alloy composed of 24⁄24 parts.

Thus, “one carat is equivalent to one part of pure gold out of a total of 24 parts of metal constituting the alloy”.

In such a case 18Kt indicates that the alloy is composed of 18 parts pure gold and 6 parts other metals, and is abbreviated to Kt, or in some cases just k preceded by the number without a space between them, e.g. 18k.

Thus “24 carats” stands for the highest purity of gold (24 parts pure gold out of a total of 24 parts) indicated by the abbreviation 24kt, just as for the quantity expressed in thousandths, the highest purity is indicated by 999.9*, i.e. the parts of gold composing the alloy thus equivalent:

e.g. 24 carats correspond to 999.9 grams of pure gold out of 1000 total grams of alloy

22 carats correspond to 916.667 grams out of 1000

20 carats correspond to 833.333 grams out of 1000

18 carats correspond to 750.000 grams out of 1000

14 carats correspond to 583.333 grams out of 1000.

Concluding that, the title is the percentage of pure gold contained in 1000 grams of alloy. In practice, if we have a ring of 18kt gold weighing 10 grams, we will have contained 7.5 grams of pure gold and the remaining 2.5 grams of metals making up the alloy, in other words: 750 parts of pure gold and 250 parts of other metals.

* In chemistry, any metal or element is quantified as 999.9 pure, leaving 1 part of impurity as presumably there are no 1000×1000 pure elements in nature.

* TITLE is the amount of pure metal present in the alloy.

The TITLE can be expressed in CARAT or in MILLESIMES.

In Italy, it is mandatory to specify the title on precious objects by means of a hallmark or mark specifying the amount of pure metal contained in the object. These legislations may vary from state to state.

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