SILVER, HOW IT IS ALLOYED, TITLE OR THOUSANDTHS
Silver chemical symbol Ag – atomic number 47 – specific gravity 10.5; is a chemical element that occurs in nature both pure and in the form of ore (argentite). It is used in jewellery, silverware, for minting coins and medals and in photography.
It is part of the ‘noble metals’ group, and are those metals that have the following chemical-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.
Known since antiquity, in Greek it means ‘shining white’. It is a lustrous white, soft, ductile and malleable metal, and is the best conductor of heat and electricity of all metals.
In its pure state it is very soft and is therefore mainly alloyed with copper and in some cases with aluminium.
As a noble metal it does not oxidise, and is also used in the pharmaceutical industry for its antiseptic properties, it is attacked by nitric acid, sulphur and its compounds.
Around 10,000 tonnes per year of Ag are mined in the world’s major mines, with the largest deposits in the USA, Canada, Spain, Bolivia and Norway.
It has a melting temperature in its pure state of 960°C, and excellent thermal and electrical conductivity, with good resistance to stress (breaking load 40 Kg/mm2 ), it welds easily, it is very soft and tough, and it is easily modelled because it is very ductile and malleable, these two chemical properties indicate the metal’s ability to be reduced into sheets and wires.
In the gold-silver sector, silver is alloyed with copper and the main titles* most commonly used are: 800/1000, 900/1000, 925/1000, the first used in silverware mainly for its mechanical properties and hardness, for cutlery, crockery, tea and coffee services, the second so called coinage silver, for medals, coins and some ornamental objects, the last defined as quality silver for jewellery and wearable jewellery; and in the last 50-60 years it has also often been used in its pure state, for its shining colouring, to make artist’s objects and jewellery, i.e. real works of contemporary art.
Other uses of silver in industry and crafts are: silver plating galvanic process to coat other metals and silver itself, to make mirrors, and used in photography because silver salts (silver bromide) are sensitive to light.
* TITLE is the amount of pure metal present in the alloy.
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.
For Ag is usually expressed in thousandths e.g. 800/000 or 925/000, which means that an Ag alloy of gr. 15 at 925/000 contains gr. 13.87 of pure Ag and gr. 1.13 of pure Cu, likewise, an Ag alloy of gr. 15 at 800/000 contains gr. 12.00 of pure Ag and gr. 3.00 of pure Cu.
Pure silver is quantified as 999.9/000.
HOW TO PREPARE AN ALLOY ?
The formula to prepare a silver alloy is very simple, having 13.87 gr. of pure Ag how many gr. of Cu ( Copper ) must we add ?
Weight pure Ag x 1000 : title = alloyed Ag
Alloy Ag – Pure Ag = Cu
e.g. 13,87 x 1000 : 925 = 14,99 (15,00)
15,00 – 13,87 = 1,13
in conclusion to bind 13.87 g of pure Ag we must add 1.13 g of Cu ( Copper )
and if we want to know how much Ag and how much Cu is contained in gr.15 of alloy 925/000?
Weight Ag alloy x title = Pure Ag
Weight Ag alloy – pure Ag = Cu
15 x 925 = 13,87
15 – 13,87 = 1,13
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