18ct gold vs 9ct gold
Is 9 ct gold more durable than 18ct gold? This is a question we get asked again and again at Metal Urges Fine Jewellery. The simple and correct answer is NO! Many of our new clients are surprised to hear this answer. The commonly held opinion of many (including lots of people in the jewellery trade) is that 9 carat gold is harder, and therefore wears better than 18 carat gold. At Metal Urges we believe in the saying "Knowledge Is Power" and take satisfaction in empowering our clients with correct information and knowledge! So here goes…
The reason people believe 9ct gold to be more durable than 18ct gold is simple… there is confusion between the two terms 'Hardness' and 'Durability'. The following simple example generally helps explain the difference best:
If I lean a pane of glass up against a wall and then place next to it a sheet of perspex (hard plastic sheeting). The glass is clearly the harder material by any hardness test you wish to carry out! Ok now we give each piece of material a good kick. The results are obvious… the glass shatters and the perspex flexes and survives. The harder glass sheet proves less durable than the softer perspex. So it is with 9ct and 18ct gold.
9ct gold is clearly the harder material when compared with 18ct gold… it is this harness that reduces 9ct golds duability when it comes to everyday knocks and wear and tear. Any jewellery sales person who tells you that is 9ct gold is more durable or longer lasting than 18ct gold is either leading you astray intentionally or like the masses simply does not understand the difference between the terms 'hardness' and 'durability'.
Pure gold is a beautiful rich yellow metal worshiped and highly prized by many societies throughout human history. It is well known and accurate to say that pure gold is a soft but highly durable metal not suitable for most jewellery manufacture. Some cultures do prefer pure gold, or near pure gold (22ct) jewellery and pay for it either by decreased durability, or financially by making pieces extremely thick and heavy to add strength to designs so they don't get pushed out of shape through wear!
Pure gold is combined or 'alloyed' with other metals to add strength, and hardness . The amount and type of other materials (alloys) added determines the final carat (gold content) of the gold alloy. There are many different recipes for gold alloys, for our purposes we will just describe the more common jewelry alloys.
24ct (twenty four carat) gold is pure gold, so all 24 parts are pure gold. Soft and extremely durable.
18ct gold is 18 parts pure gold or 75% pure, hence the stamp 750 found inside pieces made from this alloy. This is the main metal used at Metal Urges Fine Jewellery & Diamonds, it is strong, beautiful, durable and does not tarnish, corrode or react with its owners skin. This is an ideal metal alloy for making pieces such as engagement and wedding rings that need to last at least a lifetime!
9ct gold is 9 parts pure gold or 37.5% pure, hence the stamp 375 found inside pieces made of this alloy. Due to this metals lower durability and tendency to tarnish, corrode and react with its wearers skin, Metal Urges choose not to work with it. An engagement ring made from 9ct gold can not be expected to last more than a lifetimes normal wear.
The obvious question here is… why would an alloy like the 375 above even be labeled as gold. Would it not be more accurate to call it by the name of its other much larger % component alloys? It is after all only just a little over third pure gold!
Ok so now we come to the confusing bit!
Pure gold is soft… CORRECT!
Therefore the more other metal (alloys) we add, the more durable it becomes… WRONG!
This is a common and understandable mistake to make, both consumers and many jewellers within the trade have commonly made the same mistake over a long period of time. This mistake has become lazily accepted as the truth.
The truth is that the alloying of gold is an incredibly complicated process when it comes to generating fine alloys for jewellery production. If you ask at Metal Urges we are very happy to run through the process and show you our alloying area and recipes. Unlike most Australian Jewellery businesses, we mix our own metals, allowing us much finer control of our end product. Each different alloy has its own characteristics including colour, workability, hardness and durability. It is quite possible to make harder or softer alloys of 9ct and 18ct golds than the common alloys found in most commercial jewellery. This is useful, as we often find that different components within a piece require different hardnesses and workabilities. The ability to control our materials will see our jewellery pieces last longer and become heirloom jewellery for future generations.
The other major factor affecting gold alloy hardness is how the material is worked after alloying. Some gold alloys can be hardened through the manufacturing process. This is called 'work hardening' and is normally the result of compression and or the alignment of the metal molecules within the material. As a general rule: materials that have been work hardened last longer and wear harder than those that have not. A work hardened alloy can be somewhat softened again through the process of annealing. This involves heating and cooling the particular alloy involved through a certain cycle. Different alloys require different treatment to achieve this. Just to make things really complicated: Maximum hardness doesn't necessarily mean maximum durability! An in depth knowledge and understanding of each alloy is required. At Metal Urges we pride ourselves on our current depth of knowledge and continuing quest for further understanding.
Due to the inert nature of pure gold, 18 carat alloys are almost completely resistant to corrosion in typical everyday use. In stark contrast, 9 carat alloys are much less resistant due to their low pure gold content, and will quickly turn dull or blacken when in contact with perspiration, some clothing, regular household chemicals, and even the atmosphere. Not all that appealing for an exclusive custom made engagement ring! This is one of the main reason Metal Urges will not work in 9ct gold alloys.
In conclusion, we at Metal Urges Fine Jewellery strongly believe that if there we were to be limited to only one gold alloy… we would love it to be 18ct gold! Its excellent all round properties make it indispensable for the production of fine handmade, designer, art jewellery!
And then there is the differences between platinum, paladium and 18ct white gold… but that's another day on the blog!