In its pure form, gold does not rust or tarnish.
Yet, most gold items and jewelry will lose their shine and sparkle to effects of gold corrosion such as rust spotting and surface tarnishing.
This article explains everything you need to know about gold rust spots, gold tarnish, and how to keep your gold jewelry lustrous and shiny.
Corrosion in Gold Explained
In truth, gold corrosion is pointless to define, making any attempts to explain the phenomena somewhat counterintuitive.
Corrosion, in general, is the chemical change process that results in the gradual deterioration of reactive elements when exposed to specific chemical substances.
Rusting, for instance, is the electrochemical process that results in the corrosion of iron or its alloys when exposed to oxygen.
This process is typically sped up by moisture in the air.
Tarnishing, on the other hand, though similar to rusting, occurs only in non-ferrous metals such as aluminum, brass, copper, nickel, and magnesium.
Unlike iron, nickel, and brass, pure gold does not react with oxygen, and it will neither rust nor tarnish.
Other metals that are described as least reactive chemical elements include platinum and palladium.
They belong to a group known as noble metals.
Gold and other noble metals neither experience rusting nor tarnishing in their pure forms.
Brass, copper, iron, and other metals are highly reactive chemical elements belonging to the group base metals.
Most gold items contain tiny particles of base metal -typically copper, nickel, or silver- which may cause tarnish or ‘rust spots’ when the alloying metal reacts with oxygen and sulfur compounds.
Fashion gold jewelry is rarely struck in pure gold because of the yellow metal’s soft and malleable nature.
Manufacturers usually alloy gold with other metals for three primary reasons:
- Strengthen the form
- Improve durability during wear
- Affordability
Alloying comes at the cost of reducing the purity of the gold and thus making it susceptible to corrosion.
Something important to note here is that the extent of corrosion in gold depends upon the proportion and type of base metal used in the gold alloy.
Note that gold will readily form an alloy with any non-ferrous base metal but only blends with ferrous base metals about as well as water mixes with oil.
As you would likely guess, gold will not rust even in alloy form as no iron is used in creating it, and only iron-specific oxidation results in rust.
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Understanding Gold Purity & Gold Tarnish
Gold purity is measured in parts of 24 called carats/karats, and gold fineness is given in thousandths, where is 24 karat or .999 gold is pure gold.
As pure gold or (24 karat gold) does not show signs of corrosion, any gold item that does not stay shiny due to surface tarnish is lower karat gold.
Tarnished gold loses its luster only because it is alloyed using base metals that have tarnishable properties.
Tarnished gold isn’t necessarily fake gold.
You will see more tarnishing in gold alloys containing a more significant proportion of the base metal than the pure gold itself.
There are minimum legal requirements for the percentage of pure gold versus the alloying base metals.
The minimum proportion of pure gold in gold items in the UK and US is 37.5% (9 karats) and 41.7% (10 karats), respectively.
Anything lower in gold karat cannot be considered gold in the US and UK precious metals market.
Austria, Ireland, France, and Portugal accept 9 karat gold as a minimum legal requirement, but a few other countries in Europe treat lower karat gold jewelry as gold valuables.
These minimums are not a guarantee that your gold jewelry that meets the requirements won’t tarnish.
In fact, experts recommend higher karat gold if you are in the market for gold jewelry that is less likely to show signs of corrosion.
You will see less tarnishing in jewelry struck in the range of 14 – 18 karat gold.
Since most gold jewelry is manufactured in the range of 8 -10 karat gold to make it affordable and hard to experience wear, they have much less luster and may tarnish quickly.
Gold rounds, bullion coins, and bullion bars, on the other hand, are typically struck in high karats of gold and will experience tarnish at a much slower pace – if at all.
Some of the world’s most popular gold bullion coins are minted in 22 karat gold, which means that they contain 91.67% gold making up the troy ounce weight stamped.
- South African Krugerrand gold coin,
- US gold Eagle coin,
- British Sovereign gold coin
Metals like silver and nickel make up the remainder of the coins’ proportion and additional weight.
The point here is that these gold coins are highly regarded as part of investment assets and are generally viewed as a store of value, yet they are susceptible to some form of corrosion.
Though rare, some really old gold American Eagles and British Sovereigns may appear to vary considerably in terms of their color, with most having a dull finish depending on how they were stored over the years.
Restoring Tarnished Gold Jewelry
There are many ways to restore the shine to your gold jewelry, but we recommend taking it to an expert for thorough but safe cleaning.
Jewelers may only suggest methods for cleaning lower carat gold jewelry.
Do not try to clean your 22-carat gold or higher karat pure gold bullion coins or bars, as this action may damage the underlying metal and negatively affect the value of the item in the market.
When cleaning your gold jewelry, avoid using agents that have been shown to be highly abrasive. Never use toothpaste or baking soda.
Here’s how to clean your tarnished gold jewelry at home:
- Mix a few drops of mild shampoo into a bowl of warm water
- Use the detergent to clean the tarnished part with a soft-bristled brush gently
- Rinse well and allow to air dry completely
- Use a soft cotton cloth or jewelry polishing cloth to shine your gold jewelry
- Store your gold jewelry properly in a moisture-free box
- Silica gel packets help maintain a moisture-free environment
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