Gold is a dense inert bright yellow element that is the most malleable and ductile metal, occurring in rocks and alluvial deposits. The radioisotope gold-198 (radiogold), with a half-life of 2.69 days, is used in radiotherapy. Symbol: Au; atomic no.: 79; atomic weight: 196.97; valency: 1 or 3; relative density: 19.32; melting pt.: 1063°C; boiling pt.: 2966°C.
Gold and jewellery are synonymous, partly because of its use throughout history covering more than 6000 years. Its unique position of importance is not simply due to its rarity, but also its appearance and the character of the metal itself. In its pure 24 carat form its colour is a unique bright yellow which when combined with its high lustre has connected it with the sun in ancient times. Because it is practically chemically inert it does not oxidise in air and retains its high lustre.
Gold is also the most malleable and ductile of all metals and can be beaten to a transparent film approximately 0.000005mm in thickness and is used as an anti-ice and anti-mist unit when sandwiched between laminated glass in the aircraft industry.
One Troy ounce of gold weighs 31.1035 grams. One ounce of gold is accepted to mean 31.1 grams of pure 24 carat gold although in reality it is likely to be 0.9999% pure, often called fourn nines. Imperial ounces, equivalent to 28 grams, are never used.
Practically all the gold in the world is mined. To produce one troy ounce (31.1035gms) of gold from a rich mine, about three tonnes of ore are blasted from the reefs, conveyed to the shaft, hoisted to the surface, crushed to the consistency of powder and then passed through the processes of agitation, filtration, and then treatment with potassium cyanide ( KCN a white poisonous granular soluble solid substance, much used in the jewellery trade) to separate the metal. The production of this small amount of gold requires more than 5000 litres (5 tonnes in weight) of water, 750 KWh (approx £50 in the UK at 6.5p per unit but industrially the figure is significantly less) of electricity, explosives, chemicals, compressed air and 39 man hours.
For most uses of gold the pure metal is too soft on its own and is therefore hardened by the addition of alloying elements, copper, silver, nickel, palladium and zinc. Gold is of course yellow and the various colours seen such as red, white and green are simply alloys of gold. The final colour is dependent on the ratios and type of alloys added.
Gold is yellow, copper is reddish, and all other metals are a silvery grey in colour. There are however gold alloys, that is mixes of differing metals, that appear grey/white.
White gold (alloy) became popular around 1920 as a substitute for platinum, as platinum was quite expensive. Simply mixing a white and yellow metal together will not produce a colour in the same way that mixing paint does. The most common metal used to 'bleach' gold is nickel which is both inexpensive and provides a good platinum look-alike in 18ct alloys. It has however been linked to dermatitis through allergic reactions with the skin. It has also been suggested that it may be slightly carcinogenic. A recent E.U directive has indicated that soon all jewellry will have to be nickel safe with only a few ppm being allowable.
A typical white gold alloy might be
18ct gold 0.750, copper 0.055, nickel 0.145, zinc 0.050
A typical nickel free white alloy might be
18ct gold 0.750, copper 0.040, silver 0.040, palladium 0.170
Palladium is the next choice for use in white gold alloys and, apart from its high price and high melting point (1552 degrees celsius), is an ideal alloy. Its higher base cost and workshop recovery costs make for a more expensive product but the advantages of a non nickel alloy now out weigh these factors. Platinum, chromium, cobalt, zinc, tin and silver are all used as whiteners. Silver has excellent working properties but is poor as a whitener. Copper is also added to improve the ductility of most white alloys.
It is important to remember that even the best white gold alloy is actually grey, as is platinum. The white finish you are accustomed to is a rhodium plating.
Rhodium is a hard corrosion-resistant silvery-white element of the platinum metal group, occurring free with other platinum metals in alluvial deposits and in nickel ores. It is used as an alloying agent to harden platinum and palladium. Symbol: Rh; atomic no.: 45; atomic wt.: 102.90; valency: 1-6; relative density: 12.4; melting pt.: 1966°C; boiling pt.: 3727°C (approx.).
It is usual to rhodium plate all white gold jewellery in the UK and some platinum. Rhodium is very bright, hard, and highly reflective and when applied by an electrochemical process to white gold it forms a hard white highly reflective surface to the metal. This is the polished white surface which you associate with platinum jewellery. When the rhodium plating wears through the colour of the actual alloy can be seen. This varies from a yellowish grey to a plain grey. On some cheaper jewellery, particularly 9ct, one piece castings are made from a yellow alloy. The highlights or head of a ring is later made white by 'stopping off' the yellow parts with something akin to nail varnish and rhodium plating the rest. The mask is then removed to leave the two colour item.
This is the 'how long is a piece of string' question. The answer depends on how thick the plating is, and how much wear the item is subjected to. An average is perhaps several years, but it can be as little as a month and we have seen rings make it beyond twenty years.
Platinum is a ductile malleable silvery-white metallic element, very resistant to heat and chemicals. It occurs free and in association with other platinum metals, especially in osmiridium: used in jewellery, laboratory apparatus, electrical contacts, dentistry, electroplating, and as a catalyst. Symbol: Pt; atomic no.: 78; atomic weight: 195.09; valency: 1-4; relative density: 21.45; melting pt.: 1772°C; boiling pt.: 3827°C (approx.).
Pure platinum works beautifully, it can be readily welded and soldered and takes a lustrous polish, but unless it is finished a heavily cold worked state, it is too soft for hardwearing jewellery. Small amounts of certain alloying elements can give platinum the properties that make it ideal for jewellery. Copper, cobalt, gold, iridium, palladium and ruthenium alloy easily with platinum.
Opinions differ on the difficulty of polishing platinum, although once well polished it maintains its finish virtually tarnish free for ever. As with any metal, the polished surface of some platinum alloys may scratch with every-day wear. Matte finish platinum tends to burnish and highly polished platinum tends to matte a little. With reasonable protection from knocks and abrasion, highly polished platinum can be brilliant and kept that way. A large proportion of platinum-palladium alloy is plated thinly with rhodium, which scarcely alters the colour but does impart some extra wear resistance.
This is a classical myth. Actually 9ct could be harder but normally it is not. The hardness depends on many factors including both the mixture of alloys and the way the product is treated during manufacture. In general most 18ct carat alloys are both harder and more durable than their 9ct counterparts. 9ct is also usually more brittle than 18ct. If the gold is worked by rolling, hammering, bending and stretching it becomes 'work hardened'. This usually leaves the metal in a more brittle state and less suitable for wearing. By a process of heating called annealing which removes internal stress, crystal defects, and dislocations, the metal regains its former malleability. This may be carried out many times during the manufacturing of a hand made piece, but as most jewellery is cast today, this happens only once.
Probably not, that is not gold itself. What people occasionally have is an allergy to the nickel content in gold alloys, usually in the alloy rich 9ct golds. 9ct alloys go dull or even black from the exposure to chemicals in the atmosphere and also may discolour from contact with perspiration, bleach, household chemicals and some fabrics.
Detergents and other chemicals lodge between rings and the skin causing problems, particularly hairspray, beauty and cleaning products. Antiperspirants exacerbate metal allergy problems. It has been suggested that the sweat of a healthy person after exercise contains 18 times the nickel content of blood. The antiperspirant reduces the bodies natural way of eliminating heavy metals and can lead to a build up in intensity, which causes a higher concentration in the sweat than is normal.
The most common type of allergy we encounter is a phantom allergy caused by a noticeable desire to upgrade to 18ct or platinum!. As nickel and zinc are not used in 18ct alloy, just silver and copper, it is unlikely to produce any kind of allergy problems.
Hallmarking is the application of a quality control mark to an article of precious metal. It is also called an assay or standard mark. They are usually applied after accurate independent testing by one of four UK assay Offices which are legally empowered to test precious metals and apply a hallmark to them. These offices are Birmingham, Edinburgh, London and Sheffield.
The history of gold and silver quality standards goes back to the early uses of these metals as money. Legal regulations governing the marking of jewellery began here in the UK in 1239 and in one form or another have existed throughout the civilised world since. Penalties for violation of these laws have varied. In 1397 a report was made on the false counterfeit stamps of two goldsmiths who were sentenced to be placed in the pillory at Westminster with their ears nailed to it and with a ticket over their heads upon which their offences were written. They each later had one ear cut off, were imprisoned and fined 10 marks.
A hallmark indicates that an article has been independently tested at an Assay Office and guarantees that it conforms to the legal standards of precious metal content, known as the fineness.
A hallmark indicates at least three facts:
Who made the article (makers mark)- the initials of the maker
What the metal is, and its purity - the fineness mark
Where it was tested (Assayed) and marked - the Assay Office mark
The Leopard's Head is the mark of the London Assay Office and has been in continuous use since 1300, when the Wardens of the Company were given responsibility for marking gold and silver wares, which passed assay, with the King's mark of the Leopard's Head. A handy guide to hallmarks from the different Assay Offices can be purchased quite inexpensively from your local bookstore.
The fineness of the precious metal content of jewellery and silverware is expressed in parts per thousand. Sterling silver is indicated by 925, which means it is 92.5% silver or 925 parts of silver in every 1000 of the silver alloy.
The current legislation is the Hallmarking Act 1973. Following amendments to the Act in 1998 and January 1999, the sponsor's mark, fineness mark and Assay Office mark remain compulsory. But the letter indicating the year of hallmarking, which had been in use from 1478, is now a voluntary mark, as are the traditional fineness symbols, the Lion Passant for 925 Silver, Britannia for 958 Silver and the Orb for 950 platinum. Platinum was only recognised as a hallmarkable precious metal since 1976.
The standards of fineness are:
Metal:
Compulsory Mark
9ct gold
375
14ct gold
585
18ct gold
750
22ct gold
916
99% pure gold
990
99.9% pure gold
999
800 grade silver
800
sterling silver
925
Britannia Silver
958
99.9% pure silver
999
85% Platinum
850
90% Platinum
900
95% (UK standard) Platinum
950
99.9% pure Platinum
999
An article cannot be described as being of gold, silver or platinum unless it is hallmarked, or the article weighs less than 0.5 grams in platinum, 1 gram in gold or 7.78 grams in silver.
There is no substitute for having your finger measured professionally, but it's not an exact science. Our fingers change in size from morning to evening, month to month and even Winter to Summer. The following chart is helpful to see how the sizes are compiled.
UK:
Diameter mm
Circumference mm
A
11.5
36.25
B
12.3
38.64
C
12.7
39.90
D
13.1
41.15
E
13.5
42.41
F
13.9
43.67
G
14.3
44.92
H
14.7
46.18
I
15.1
47.44
J
15.5
48.69
K
15.9
49.95
L
16.3
51.24
M
16.7
52.46
N
17.1
53.72
O
17.5
54.98
P
17.9
56.23
Q
18.3
57.49
R
18.7
58.75
S
19.1
60.00
T
19.5
61.26
U
19.9
62.52
V
20.3
63.77
W
20.7
65.00
X
21.1
66.29
Y
21.5
67.51
Z
21.9
68.77
Z+1
22.3
69.99
Z+2
22.7
71.31
Z+3
23.1
72.57
Z+4
23.5
73.83
Z+5
23.9
75.08
Z+6
24.3
76.34
Z+7
24.7
77.60
Z+8
25.1
78.86
To calculate:
American size= (diameter-11.54)/(0.83)
Japanese size= (diameter-12.67)*3
European size= circumference-40
What is Gold?