Gold and platinum will not change in colour even if they are exposed to sweat or wearing in hot springs. They are highly corrosion-resistant and acid- alkali-resistant metals. So, since gold and platinum do not oxidize, why do jewellery made of these two metals still change colour? This time we will introduce to you why jewellery changes colour due to oxidation, as well as the handling methods and precautions. I hope after reading it, you will be able to carefully protect your favourite jewellery and use it for a long time!
Will gold and platinum oxidize?
Gold and platinum are considered as a very stabilize materials. It is stable to the point that there is no other solution that can dissolve them except the “Aqua regia” (a special solution made by mixing concentrated hydrochloric acid and concentrated nitric acid). Since it does not react with other substances, therefore they will not have the problem of oxidation. Because they have the characteristics of high scarcity, high price, and will not oxidize or rust, they are called precious metals.
In addition, although the higher the purity, the less discoloration, in contrast the higher the purity, the softer it is, the easier it is to deform, and the weight will become heavier. The density of platinum and gold is quite high, with a weight of 20 grams per cubic centimetre. Therefore, these two metals are not suitable for use in jewellery that needs to be crafted in detail.
The purity and colour of gold
The unit of gold purity is “k” (carat), and 99.99% purity is marked as k24, and it can also be expressed as 24k or 24k gold. K22, k20, k18, k12, and k10 indicate that the gold content decreases in order. When it drops to k10, it means that the gold content of the product accounts for less than half of the whole.
The purity of platinum
Platinum uses “pt.” as its purity unit, and pure platinum is pt1000. 95% platinum content is marked as pt950, and 90% is marked as pt900. The higher the purity, the more expensive it is. Palladium is the metal material most used to synthesize alloys among platinum metals.
Why does jewellery change colour?
The most common cause of discoloration is that the jewellery encounters oxygen, sweat, sebum, or chemicals such as detergents, shampoos, and hot spring ingredients, etc., causing a reaction to cause discoloration.
Gold or platinum will not change colour in daily life. However, as mentioned above, because the higher the purity of gold or platinum, the easier it is to deform, so it is usually mixed with other metals. Even gold and platinum jewellery will change colour because the jewellery contains less gold and platinum, and the other metals used in the mixture are oxidized, which causes jewellery to change colour.
If you want your jewellery not to change colour easily, it is recommended to choose K18 gold products or platinum products above pt900.
My jewellery has oxidized and changed colour, what should I do?
If the jewellery on your hand has changed colour, what should you do and what are the precautions?
Wiping diligently with a soft cloth or cleaning with a neutral detergent can effectively prevent jewellery from discoloration. Since the sebum or sweat residue on the jewellery can easily cause oxidation, the best way is to wash it immediately after each use. If the jewellery has changed colour, it is the most effective method to remove the chemically reacted part. You can buy abrasive cloths for precious metal grinding at hardware stores, and you can use abrasive cloths to carefully grind off the discoloured parts.
Note: Please confirm the engraving of the jewellery before maintenance!
Due to the different materials and processing methods of jewellery, maintenance methods and precautions are also different. Although gold or platinum gives the impression of being durable, please do not forget that they are incredibly soft metals. The thinner and thinner it is, it may affect its tensile strength. Special attention should be paid to the fact that if GF (gold-clad), GP (gold-plated), PP (plastic electroplating), WG (rhodium-plated) and other marks are engraved on the jewellery, it means that the jewellery has been electroplated and polished. It may cause the plating process to peel off. Finally, if there are gems inlaid on the jewellery, be careful not to damage the gems when grinding. For extremely valuable or precious jewellery, it is recommended to consult the store where you purchased it directly.