About Precious Metal Alloys & Plating

1. Sterling Silver

2. Argentium Silver

3. 9K Yellow & Rose Gold

4. 18K Yellow & Rose Gold

5. 9K & 18K White Gold

6. Platinum

7. Hallmarking Precious Metals

8. Precious Metal Plating & Gold Vermeil

Most people are familiar with the periodic table of the elements. While each material represented on the table is considered an element, they are not all metals. For our purposes we will only focus on a small number of the transition metals and germanium. When two or more metals are combined at melting temperatures, they form what is called an alloy, which has its own unique crystal structure and properties. Adding one metal to another can lower the melting point of both, as in the case with copper and silver, or it can make a brittle metal more malleable, or bleach out an undesirable colour as in the case of white gold.

People often confuse the carat, abbreviated ct. with karat, abbreviated K, and this misunderstanding of the term has become so commonplace that they have almost become interchangeable. Carat (ct) is a measure of weight and refers to the unit of measure used to weigh gemstones. The word karat (with a K) refers to the number of parts in 24 of a gold alloy which is pure gold (24K).

9K therefore has 9 parts Au in every 24, 375 parts in 1000 or can be considered to be 37.5% pure, 14K will be 58.5 % pure, 18K 75% pure, and 22K is 91.6% pure.

1. Sterling Silver

Sterling silver consists of silver and copper. The addition of copper lowers the melting point below that of both metals in their pure form, and adds strength to the otherwise very soft fine silver. But with the good comes the bad, and the copper content is what causes sterling silver to tarnish more quickly than pure silver would, and it also reacts to oxygen when a flame is applied meaning that working with it requires a bit more elbow grease.

2. Argentium Silver

Argentium silver is a proprietary alloy similar to sterling silver, but the addition of germanium prevents the formation of firescale, making it easier to finish and thus uniquely suitable for projects that require laser engraving. It does tend to slump when heated and crack during hand forming though, and it is more expensive which is why it is not widely used.

3. 9K Yellow & Rose Gold

Commonly used gold alloys in the jewellery industry include 9K yellow and rose gold, which consists mostly of gold, silver, copper and zinc in varying combinations. This is the most affordable alloy, and most commonly used in South Africa, although it is not very popular elsewhere in the world.

 4. 18K Yellow & Rose Gold

18K yellow and rose gold alloys are mostly a combination of gold, silver and copper. The more copper is added, the redder the metal, but also the more brittle, the more silver is added, the yellower the metal, and the more malleable it will be. 18K yellow and rose gold is darker than their 9K counterparts and generally softer.

5. 9K & 18K White Gold

Then we get to white gold and this is where things get complicated. White gold, being an alloy of metals and not an element in its own right, means that the yellow of the pure gold needs to be bleached out of the alloy by the addition of white metals. This is tricky because the properties of metals change as more elements are added. White gold therefore consists mostly of the same alloys as yellow gold, but with the addition of either palladium, nickel or platinum to bleach out the yellow. This of course means that the resulting alloy is not entirely white. In the not-so-distant past we used to rhodium plate white gold to give it that pure white finish, but after the price of rhodium skyrocketed, this step was replaced with other metals or omitted altogether.

Nickel white gold alloys are an issue, because most people are allergic to it, so that alloy is dropping out of use almost entirely except for mass produced jewellery. The platinum alloy is also not too popular due to platinum’s temperamental behaviour and the higher temperatures required to work with it. That leaves us with palladium, which for decades has been the preferred alloy. It is whiter than other white gold alloys, works well, hold’s its shape and is a bit more resistant to wear than other alloys.

Why do we use white gold at all?

Though white gold alloys have existed for as long as 400 years, they didn’t become popular until jewellers in the USA were banned from using platinum in jewellery during WWII so that all the reserves could be allocated to weaponry, where it is used as a catalyst in explosive devices.

Currently there are 16 different alloys of white gold available for purchase in South Africa. Each alloy has different properties and different applications. Some are easier to cast with and others are better for bench work. However, all of them are mixed according to closely guarded and often patented formulae, which require sophisticated equipment to unravel.

5. Platinum

Platinum is used almost entirely pure. The 5% alloy is usually just one other metal and that is usually copper, or gold, or ruthenium. Platinum does not play well with most metals and contaminates easily. When the metal is contaminated it has to be sent away for refining and the project has to be started over with fresh metal.

6. Hallmarking Precious Metals

Hallmarking is the practice of marking the inside or back of an object manufactured from precious metals with the fineness or purity of the metal alloy, and depending on local laws also a mark indicating its origin and the maker's mark (logo or other identifying mark unique to the manufacturer).

Hallmarking law differs greatly from country to country, and although all countries require hallmarking of some kind, all authorities are not equally concerned with establishing the authenticity of the hallmark. In Britain, hallmarking is exclusively done by the assay office, which has a whole list of things that need to be noted on the item, each represented by a symbol.

South African law allows the creator to hallmark their own work but requires that all precious metal articles weighing more than one gram be stamped or impressed in some way with a hallmark showing the fine metal content, as well as the letters ZA. Previously this was required to be inside an oval, but that regulation has been scrapped, we now only use the ZA by itself.

Since carat with a "c" and karat with a "k" have become almost interchangeable terms, you will see both hallmarks appear in jewellery. The parts per 1000 is also commonly used as a hallmark, and can be used for all metals, while karat only applies to gold.

Sterling silver is marked 925 or SIL, while fine silver would always be stamped SIL. Argentium is marked 935 or 960 depending on its fine silver content.

Platinum and palladium are often written out, abbreviated, or expressed as a number of parts per 1000. 555 is an alloy of platinum which is commonly used in other parts of the world, but in South Africa we use 950.

8. Precious Metal Plating & Gold Vermeil

Plating, or more accurately, electroplating, is the process of depositing a layer of one material in solution onto another material which is in a solid state, with the help of electrical current. This can alter the optical colour of a material and is useful in creating a more luxurious look at a more affordable price.

Plating can be deposited onto a precious metal base or bases consisting of non-precious metals, referred to as "base metal", as well as stainless steel.

For jewellery applications we make use of a variety of metals for this purpose. The most commonly used is gold plating. Gold plating is available in both yellow and rose gold, and the layer deposited onto the solid article is between 0.175 and 0.500 microns thick. At Surita du Toit Design Atelier, gold plating is always deposited onto a sterling silver or Argentium silver base. This means that even though the colour may fade over time as the article is exposed to skin oils, chemicals and environmental factors, the finish can be 100% restored to its former luster, something which is not possible with base metal or stainless steel.

White gold articles are commonly plated with either Whitenor (a proprietary mixture of metals producing a white finish) or palladium, no longer rhodium as was the case in the past. This gives the metal a pure white finish and can be restored 100% to its former luster.

Gold vermeil is a different kind of gold plating which requires special conditions, a different chemical solution and longer exposure time than gold plating. In order for the plating to be referred to as gold vermeil, it must be deposited onto sterling or Argentium silver, and must be thicker than 2.5 microns. This creates a durable and long-lasting finish which can be restored 100% to its former luster.