Gold and Platinum, what is the difference ?

As a Jeweller I am continually asked about the differences in metals used in creating the pieces I do. 

Which should I use ? 

Why does White Gold need Rhodium plating ?

Which metal will last the longest ?

And on they go, so I will try to clear up some of those and more in this short explanation piece for you.

YELLOW GOLD
Gold in it's pure form is given the rating of 24 Carat, at this stage is it generally regarded as too soft to be a practical metal for making Jewellery. To improve on this and improve its durability we 'alloy' it with other metals. This in fact is the process of diluting the 24 Carat gold into a lesser purity by adding both copper and silver, the metals are melted together and then cooled to solidify into a new 'alloy'. The amount of copper and silver added will determine the actual new Carat that is created. This alloying actually hardens the metal and makes for a much better result when making Jewellery.

Remembering pure Gold is 24 Carat, we take the purity into a percentage scale based on 1000 instead of 100, 24 Carat is 1000%, its usually regarded as 999.9% pure but we will round it up to explain.
If we use the simple multiplication of 10, 100, 1000 we can explain the differences quite easily.. 

18 Carat is 75% pure Gold with 25% Copper and Silver added.
14 Carat is 58.5% pure Gold with 41.5% Copper and Silver added.
9 Carat is 37.5% pure Gold with 62.5% Copper and Silver added.

This will also explain the markings stamped on Jewellery, 750 is 18 Carat, 585 is 14 Carat, and 375 is 9 Carat going back to our 1000% use. Remembering that each Carat is a percentage of 24..... 
24 x 75% is 18, 24 x 58.5% is 14 and so on. It all ties in easily if you read it over again..

It is a world wide scale that is used without variation, the differences found relate to the preferred Carat used in within various cultures. Australia tends to stick with 18 and 9 Carat, occasionally 14 and 10 Carat are found here but generally the first two. The USA will also introduce you to 12 Carat, Asia and the Middle East will use minimum of 18 often using 22 Carat, Germany uses 8 Carat and so on,  again the purity of these metals is based on the percentages I have outlined previously. Working back, 24 divided by say 12 will give you 50% or a stamp of 500 on a 12 Carat piece.

WHITE AND ROSE GOLD
The Carat scale works exactly the same here, however when we 'alloy' our YELLOW Gold we substitute the Copper and Silver for metals that dominate the colour. Dropping the percentages of Silver and increasing the Copper results in a ROSE Colour, removing the Copper totally to change the Yellow into a WHITE 'alloy'. Generally Palladium is used but Silver and Nickel can be added to bleach the yellow colour and achieve the desired white. However, the end product can vary and the resultant colour can be a little less than perfect, often leaving a subtle yellow tinge to the white. More commonly an issue with 9 Carat than 18 Carat, the yellowish appearance is always masked with the addition of 'Rhodium Plating' over the ring to give it a brighter, whiter lustre. 

'Rhodium' is another metal that has many uses outside the Jewellery industry, however as it is part of the Platinum family and has a beautiful white lustre far superior to White Gold it makes a perfect addition to the Jewellers tools. To Rhodium Plate a White Gold piece requires the piece to be hand polished and submerged into the Rhodium solution, an electric current is then passed through the solution and submerged item. The result is a bonding of Rhodium, dissolved through the solution, onto the piece giving a beautiful lustre that White Gold itself cannot achieve. It must be remembered this is a temporary plating which will wear and require a top up depending on the treatment the Jewellery piece receives. Generally we find a 12 month timeframe is the norm.

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PLATINUM
Very much becoming the metal of choice for a lot of women, Platinum is a completely unrelated metal to Gold. A much rarer metal Platinum is also naturally white, having a comparable colour to Rhodium, so the need for plating is zero. A less malleable metal than Gold, Platinum pieces are generally hard wearing and will give greater resistance to bending. Platinum used in Jewellery will like gold be 'alloyed' but to a 90% purity, usually it is combined with Iridium. Much harder to work with than Gold due to its higher melting temperature and resistance to bending, Platinum is also a more valuable metal, these combine to make a Platinum piece more costly than Gold.

So the best choice for me ? 

Only you can determine that, Platinum gives a better colour than White Gold, is extremely strong, although scratching is still easily done. It is hypoallergenic so less chance of irritations to the skin but is more expensive to buy as a raw metal, it is harder to work with so labour costs can soar and it is denser meaning a heavier piece when finished.

Whether it's Yellow Gold, White Gold, Rose Gold or Platinum you choose, all your pieces need to be treated with respect and regular checks are required to insure repairs are kept to a minimum and issues are found early. Remember something that is on your body 24 hours a day, 365 days a year is going to wear away eventually regardless of what metal it is
constructed of, prevention is better than cure I always say. 

In finishing, my preferred metal to work with is 18 Carat Yellow Gold, but the current trend is for White metal and will be for some time more I'm sure.