susan ewington jewellery

9ct & 18ct, what's the difference?

Susan Ewington JewelleryComment

You may already know the answer to this one. Or maybe you don’t. Either way, there’s some gold to be found in this post for sure.

Welcome to the world of ALLOYS

When we talk metals (and by we, I mean jeweller folk) we talk and work in alloys. Alloys are the blended recipe of metals that make up the different carats and colours you may know - 9ct yellow, 18ct rose, 18ct white, and so on. Because pure gold is of course … yellow. So to make it white, or rose, or harder and more durable, it needs to be blended with other metals to give it the desired colour and hardness. And it gets pretty scientific. But I won’t bore you too much with that stuff, I don’t even fully understand it all myself.

I will however go into some detail for you, because at the end of the day, an informed choice is a good one.

9ct rose gold and 9ct white gold rings

9ct rose gold and 9ct white gold rings


CARATS

The type of carat the gold is, determines the purity level. So to put it simply, out of 1000 parts in the alloy ‘recipe’ …

  • In 18ct gold (stamped 750 or 18ct) there are 750 parts, or 75% pure gold content.

  • In 9ct gold (stamped 375 or 9ct) there are 375 parts, or 37.5% pure gold content.

    In Australia these are the two industry standard carats used. 14ct gold and 10ct gold is used commonly in American & Asian countries, let’s leave those out of the equation for now to keep it simple.



COLOURS

The remaining ‘parts’ (other metals used to make up the remaining percentage) are what determine the colour of the gold.

  • For yellow gold, a mixture of silver and copper is used.

  • For white gold, a mixture of white metals such as silver, palladium, platinum, and in low quality alloys nickel, is commonly used.

  • For rose/red gold, a high copper content is used.

18ct rose gold and 18ct white gold, freeform pink sapphire and white diamond

18ct rose gold and 18ct white gold, freeform pink sapphire and white diamond


PROPERTIES

The carat and colour of gold changes the properties of the metal. How it wears, how soft or hard it is, how brittle or malleable it is.

And these properties change, depending on the source of the alloy and the exact makeup of the ‘recipe’, but here are some generally common properties between them:

  • 9ct Yellow Gold: hard, hard wearing, will not dent or heavily scratch too easily, can be brittle, can oxidise (change colour on surface) over time, light to mid yellow tone

  • 9ct White Gold: relatively soft, medium wearing, will dent and scratch mildly easily, very malleable, will not oxidise, light grey tone

  • 9ct Rose Gold: hard, hard wearing, will not dent or heavily scratch too easily, can be brittle, can oxidise over time, strong coppery-rose tone

  • 18ct Yellow Gold: relatively soft, medium wearing, will dent and scratch mildly easily, very malleable, will not oxidise, deep buttery golden tone

  • 18ct White Gold: hard, hard wearing, will not dent or heavily scratch too easily, malleable, will not oxidise, mid grey tone

  • 18ct Rose Gold: hard-ish, hard to medium wearing, will not dent or heavily scratch too easily, malleable, will not oxidise, medium coppery-rose tone


A note on Rhodium plating …

Given that the natural colour of white gold is more of a grey tone, most white gold jewellery pieces are plated in the ultra white metal Rhodium. This is a surface treatment and does wear off over time, hence, the rhodium plating services offered or recommended yearly or every few years.

What is important to know, is that it is not necessary to have white gold coated in rhodium. In fact, the natural colour of a good quality white gold is grey and stormy and just beautiful! Especially with coloured stones. For more traditional white diamond pieces, or mass produced low quality white gold alloys, yes, sometimes rhodium plating is more desired. But just know that if you are having something handcrafted for you, it is totally your choice to have it plated or not.


What about Platinum?

Why haven’t I included this most noble of precious metals? Well, I was just trying to stick to gold for simplicity, but in the interests of sharing knowledge, here’s a tidbit:

In jewellery use, it is used as an alloy, but an extremely pure alloy, like generally around 90—95% pure. It’s colour is pure bright silvery white, it’s properties are extremely malleable and extremely dense. It is revered for its ability to displace rather than dent, as in, it does not wear away over time, it simply moves. The most prized gemstones, especially white diamonds, are often set in platinum.

natural unplated 18ct white gold ‘Giardinetti’ ring with sapphires and diamond

natural unplated 18ct white gold ‘Giardinetti’ ring with sapphires and diamond


RECYCLING GOLDS

When recycling old jewellery for a new piece, it is important to note that ideally, yellow golds are the easiest and best to recycle. Relatively any mixture of yellow gold pieces can be remelted together, even different carats, although sticking to one carat is preferable.

On the other hand, white golds do not like to be mixed together. To put it simply, there are far too many variables in the alloys that when different white gold pieces get remelted together, a structural imbalance can occur, making it unusable for fabrication. The only exception is if the pieces are known to be exactly the same alloy from the same manufacturer, or remelted from one exclusive piece.

Check out this make using both new white gold and recycled white gold from one old ring to make three seperate rings.

wedding band made using customers recycled heirloom 9ct yellow gold, and new 9ct white gold

wedding band made using customers recycled heirloom 9ct yellow gold, and new 9ct white gold

FINAL THOUGHTS

What would I choose for myself? Well, firstly, the colour depends on what stones I’m using, or just what mood I’m in that day 😂(seriously though, I hardly ever have time to make anything for myself, it is a total luxury!)

Carat? If it’s for me, 18ct is my absolute preference. It is denser. It has more longevity because of its malleable and forgiving properties, ie. it will not get brittle. It will repair more easily in the future. It’s colours are stunning. There is a reason that the most prized of precious gems are set in 18ct carat golds and platinum. They will stand the test of time if made well and cared for well.

However, it is more expensive. So budget should definitely be considered.

Well, that was a lot of information! I’m always happy to answer any questions of course, hit me up if you missed something you desperately want to know.