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Sunday, November 20, 2011

Gold Allergy

10:08 AM | Posted by bayan |
An allergy is a hypersensitivity to a substance that causes the body to react to any contact with that substance. 
Do I have an allergy to gold?
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.


Allergy Test KitDetergents 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 less likely to produce any kind of allergy related problems. What a good excuse! 

Tarnishing of Gold
Possible causes include:
  • Perspiration (everyone's body chemistry is different, hence this is why some are more susceptible than others); for women, the time of the month can influence their body chemistry. 
  • Perfume, hair or deodorant sprays, 
  • Tarnishing during storage (storage boxes may contain organic sulphur compounds),
  • Leaching of acid/ cleaning solutions from surface microporosity from cast jewellery; this causes corrosion locally (such porosity may even trap perspiration during wear, causing local corrosion) 
  • Preparation of vegetables such as onions and spices (many foodstuffs contain sulphur compounds and others are also acidic).
Another possible mechanism may be surface micro-porosity on the surface of investment (lost wax) cast items. This porosity may trap acids and other cleaning solutions, sprays, or perspiration and cause a local corrosion which 'creeps' over the surface of the item. 

The tarnish films formed are generally harmless although unsightly and may lead to a black smudging of the skin. Such films can be easily polished off by a jeweller to restore the bright gold colour. 

Possible solutions to the problem include: 

  • Store jewellery in a pouch or bag in a dry atmosphere (unpolluted, e.g. by exhaust fumes, solvent vapours, where possible).
  • If stored in a box or pouch or plastic bag, ensure it is free of sulphur-containing compounds (from solvents, fabric treatments, adhesives, etc.).
  • Polish jewellery regularly with a soft cloth to remove any early tarnish films, perspiration and other contaminants (sprays, etc). Clean after wear and do not put on perfume, deodorants, sprays, etc whilst wearing the jewellery
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Alternative white gold alloys

10:07 AM | Posted by bayan |
In the European Union especially, there is a demand for cheaper alternatives to white golds than the palladium whites which are 'nickel-free'. Many new alloys are coming to market, most of which rely on manganese additions as the main whitener. Some are palladium-free and others are low palladium alloys. Chromium and iron are also be used as whiteners. They tend to be hard and more difficult to process. Many of these alloys are not a good white colour, requiring rhodium plating, and many suffer cracking problems and tarnishing.
We recently tried to anneal a batch of white gold from Italy. It was so unmalliable we had to contact the manufacturer, and whilst the solution was simple, a high street working jeweller would find the new metals difficult, if not impossible to process.

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.

Rhodium Plating
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, and whatever you are told, white golds are only available in caratages up to 21 carat. It is not possible to have a 22 ct white gold!


Resistance to Tarnish 
18 carat and 22 carat gold alloys are almost completely resistant to chemical attack and 9ct alloys are much less resistant. Nine carat alloys can dull or even blacken from exposure to chemicals in the atmosphere, and might discolour in contact with household chemicals. 9ct chain is usually finished with a deeper yellow 18ct or 22ct coating by manufacturers, which is why the bright finish on a new 9ct chain gradually tones down to match other jewellery that you wear on a daily basis.
The original bright finish can usually be restored quite inexpensively by a working jeweller for little cost should your chain become chemically or mechanically damaged over the years.

Hardness 
As well as affecting physical properties, alloying gold generally increases the strength and hardness, with some reduction in malleability / ductility. The silver atom is slightly larger than that of gold, so alloying gold with silver gives a moderate improvement in strength and hardness. The copper atom is significantly smaller than that of gold and so it has a greater effect on strengthening gold than silver, as it distorts the gold crystal lattice more. Thus reducing caratage from 24 carats through 22 ct down to 18 carat gold results in stronger and harder alloys, but alloying beyond 18 ct down to 9 carat does not have much further effect.
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