Saturday, November 21, 2009

Gold (Au)

Definition of karatage in gold content for recognised international standards





It good to have some knowledge on gold. Knowing the industry standard and whether you're buying the best value for money either in terms of your dowry and 4 point gold (四点金).

Pure gold is used more for investment than decoration, and it tends to be quite vulnerable to scratching.

Alloys
Gold in its finest state (24 carat) is generally considered too soft and too malleable to use as jewellery. When craftsmen make jewellery, they mix fine gold with other metals (generally silver, copper or palladium) to create gold alloys.

This not only hardens it, but also influences the colour; white shades are achieved by alloying gold with silver, nickel or palladium, while red alloys mainly contain copper. You can make an alloy harder by adding nickel, or a tiny percentage of titanium.

Colour
Gold alloys are usually a mixture of silver, copper and zinc and the amounts of each can be varied to affect the final colour. Though gold's real hue is a beautiful warm yellow, different tones of gold can be used to define details on jewellery or add highlights. Whatever colour you choose, they are real gold. Its a matter of fashion and personal taste. :)



However, we should note that, for a given caratage of gold, varying the colour also changes other properties, such as hardness and strength. We should also note that we can obtain a wider variation in colour as we lower the caratage.

The special colours such as blue, black and purple are obtained by quite different approaches, either as special metal compounds or by surface treatments to obtain a patina.

Demand
Around 70% of gold demand is jewellery, 11% is industrial (dental, electronics) and 13% is investment (institutional and individual, bars & coins). Gold jewellery has strong "investment" attributes in all countries, and in markets such as India and Middle East is sold by weight at the prevailing daily rate with a supplementary "making charge" which varies according to the complexity of the piece. Jewellery is not used as currency in any market.

White Gold

They are gold alloys that look white rather than yellow. The white colour is achieved by careful choice of the alloying metals, which bleach the deep yellow of pure gold.

White golds for jewellery were originally developed in the 1920's as a substitute for platinum (Now platinum i say bye bye). White golds are available up to 21 carat.

Making gold white is similar to mixing colours in paints. Adding a red metal (copper) will tend to make gold red and adding a white metal tends to make gold paler and eventually white. Thus, all other alloying metals to gold, apart from copper, will tend to whiten the colour and so it is possible to make carat golds that are a reasonable white colour.

Whilst additions of any white metal to gold will tend to bleach it's colour, in practice, nickel and palladium (and platinum) are strong 'bleachers ' of gold, silver and zinc are moderate bleachers and all others are moderate to weak in effect.

There is 2 basic classes of white golds - the Nickel whites and the Palladium whites. The nickel-whites tend to have a colder white colour, whereas the palladium whites have a warmer colour. Good nickel whites tend to be hard and difficult to process. Good palladium whites tend to be soft, easy to process (but lost wax casting is more difficult) but are much more expensive, because of the price of palladium. Consequently, many commercial white alloys are thrifted in nickel or palladium and contain some copper; hence, colour is compromised. At the 8-10 carat (33.3 - 41.6% gold) level, gold-silver alloys are quite white, ductile although soft and are used for jewellery purposes.

White gold jewellery is often plated with rhodium!!!
For good technical and economic reasons, many commercial white golds are not a good white colour (usually a yellow-brownish tint) and are often rhodium-plated to improve appearance.

Rhodium is one of the platinum family of metals and has a high reflectivity and good metallic white colour and is hard with good wear properties. A thin electroplated coating is often applied to white gold jewellery to improve its white appearance.

Such a coating, if not subjected to undue abrasion, should have a lifetime of, typically, 3 years before it wears through to reveal the gold alloy underneath.

If you're allergic to nickel in white gold, DO check with your retailer that the alloy is nickel-free! Rhodium-plating should provide some limited protection, but remember electroplatings are often porous and will, in time, wear away!

There is currently no legal requirement in many countries for the retailer to tell purchasers if the jewellery is rhodium-plated. This applies to some platinum jewellery as well as white gold. Purchasers should always demand to know if their jewellery is rhodium-plated. If the jewellery is rhodium-plated, then you cannot know how white (or not) is the gold alloy underneath. A good quality white gold, with good colour, should not need to be rhodium-plated but may well be to conform to a consumer expectation.

If the rhodium plating does wear through, the jewellery can be easily re-plated through your local retailer and the good colour restored.

From the above, the best is still pure gold or 916 (VALUE FOR MONEY). But if you're like me a sucker for design, colour and best value for money. Best solution is to wait for discounts on gold (coloured or pure) for the best value for money!!!!

Source: World Gold Council

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