Precious metals, like gold and silver, are too soft in their pure form to keep their shape when used to make jewellery. In order to make them sturdier they must be alloyed with other metals.
Silver is usually alloyed with copper. Sterling silver is 925 parts silver to 75 parts copper. Copper is responsible for the oxidation of the silver alloy. If you want to read more about oxidizing and patina, go to the section on copper, further down on this page.
Recently some new alloys have become available, like Argentium, where some of the copper has been replaced with a different metal, in this case germanium. Argentium silver actually has a higher percentage of pure silver than sterling – 93,5% instead of sterling’s 92,5%. The advantage of germanium as an alloy metal is that Argentium doesn’t oxidise as quickly. The downside is that it’s very brittle when heated and will break if any pressure is applied while it’s hot. Argentium must be allowed to air cool rather than quenching in water while it’s still hot, like sterling.
There are other silver alloys such as reticulation silver which is 835 parts silver to 165 parts copper. Reticulation is a technique used to add texture to the metal by heating it repeatedly to the point where the surface of the metal starts to melt. It can produce very interesting designs with patience and practice.
It’s not possible to detect the amount of silver or gold in an alloy just by looking at it, which is why many countries demand that jewellery be hallmarked before being sold in stores. This is done to protect the buyer by giving a guarantee that the precious metal purity is as stated.
Gold alloys can be made up of more that two metals. Gold is usually alloyed with copper and silver. 100 grams of 19.2k yellow gold contais 80grams of fine gold mixed with 10 grams of fine silver and 10 grams of copper.
To make white gold the alloy includes either nickel or palladium. Due to the large amount of people who are allergic to nickel, a palladium alloy if preferred. Rhodium plating is commonly used on white gold jewellery. It served as a barrier between the skin and the nickel and also makes the metal whiter since white gold is never truly white, especially the high carat alloys. The downside is that, like any plating, it will wear off in time and new plating will be required.
White gold is harder and more brittle that the other gold alloys and harder to work with. It has a tendency to crack when it ‘s not annealed properly. The picture below shows what happens to white gold when it’s not properly annealed:
Unlike other gold alloys, nickel white gold must be allowed to air cool instead of quenched in cold water. Aside from being harder to work with white gold, since palladium is also an expensive precious metal, white gold jewellery is more expensive than yellow gold jewellery
The amount of each metal in the alloy is responsible for the wide range of different tones gold jewellery can have – green, yellow, red, rose, white. For example, 100 gr of 19,2k red gold alloy normally contains 80 gr of fine gold to 16gr of copper and 4 gr of fine silver. If we want the red tone stronger we can remove the silver and alloy the gold with 20gr of copper. So long as the percentage of gold to alloy remains the same it’s still 19,2k gold. We’re just using the alloy to change the color.
The same logic applies to green gold. By removing the copper in the alloy and using only silver, the color gets colder.
In the picture below you can see the difference in tone between rose gold and white gold ingots.
Pure gold, also called fine gold or 999 (999 parts out of 1000) is 24 carats,
The alloy with the greatest amount of gold is 22k, with 916 parts (91,6%) of fine gold to 84 parts (8,4%) of alloy metals.
There are several other gold alloys with different amounts of gold. The most common are:
– 19,2k with 80% fine gold to 20% alloy,
– 18k, with 75% fine gold to 25% alloy,
– 14k, with 58,5% fine gold to 41,7% alloy,
– 9k, with 37,5% fine gold to 62,5% alloy.
When working these metals – by hammering, bending, twisting – they become harder and more difficult to shape. This is called work hardening and is caused by deforming the crystalline molecular structure of the metal. As the metal hardens it looses elasticity and becomes easier to break. This is a very easy process to test, by bending and unbending a piece of wire multiple times in the same spot until it breaks.
To prevent breaking a piece of metal that is being worked on and so that the metal continues to be pliable, it’s occasionally necessary to anneal it. Annealing is when we heat the metal to a temperature between 600ºC e 700ºC (depending on the alloy) and then cool it quickly by quenching in cold water (except for the alloys mentioned above). This process realigns the metal’s molecular structure and it can be worked again. The annealing process requires some practice to prevent overheating that could melt the metal. A simple visual queue is when the metal turns black except for the part when the flame is hit it it, then it’s usually annealed. If it gets red (in a room with good light), it’s getting too hot. Another simple trick is to write a line on the metal with a sharpie pen. As you heat it, when the line disappears it’s gotten close to the right annealing temperature.
Work hardening can be an advantage when a component needs to withstand a certain amount of tension, such as clasps, ear wires and brooch pins. To harden the metal without deforming it you can hammer it with a rawhide, nylon or wood hammer. To harden the post on an earring you can just twist it back and forth a few times. The twisting also helps to check if it was soldered properly.
As an option, especially for wire wrapping, when no soldering is required, we can also buy wire with the necessary hardness. Many stores state the hardness of the wire – soft, half hard or hard. When it’s not stated, half hard is the most common.
The thickness of the wire also influences how difficult is is to bend. The thicker the wire, the more resistance you’ll encounter.
Different metals also have very different hardnesses. Aluminium is very soft, deforms easily and can only be soldered with a soldering iron, not with a torch. Steel is very hard and difficult to shape. The others mentioned in this post fall in between.
Copper is a base metal but it’s part of the composition of many precious metal alloys. In modern jewellery, copper is also used for it’s colour in mixed metal pieces, alongside precious metals. The warm red colour of copper has long been appreciated and used in jewellery for millennia.
Some enjoy the shiny reddish tone of copper while others prefer the dark, oxidised tone. Copper oxidises easily when exposed to oxygen. All it takes is leaving out in the open for a few days and the colour will darken. It can be brought to it’s original shiny colour easily, by polishing it with either jewellery polish or even plain ketchup. Personally, I like the mix between oxidised and the original copper tone so I tend to oxidise my pieces and then polish the highlights to bring out the texture.
Aside from natural oxidation, copper and silver can be darkened chemically with patina. There are many different chemicals that can be applied to copper to create different colours. The most common chemical used to darken both copper and silver is Liver of Sulphur (potassium sulfide) – known as “LOS” for short.
When using this and other chemicals, safety measures should be taken, such as gloves and good ventilation, because the chemicals emit toxic fumes that shouldn’t be breathed in. A chemical respirator is also a good idea and even an apron to prevent splashes from staining your clothes.
The copper or silver should also be clean and grease free because any dirt or grease (even the natural oils from our skin) can prevent the metal from oxidizing evenly.
A more natural, although messier, alternative to LOS is simple boiling an egg and, while it’s still hot, cut it into bits and place it inside a plastic box or zip-lock bag along with the jewellery you wish to oxidise. The fumes from the hot egg have the same effect as the LOS, although it’s a slower process. The egg doesn’t need to be in contact with the jewellery. It’s the fumes inside the closed container that do the job.
To maintain the shiny colour of copper or even the oxidised effect, it’s necessary to seal the metal with wax or varnish. Varnish also protects copper from humidity and prevents the chemical reaction with the skin that makes some people’s skin turn green.
Turning the copper green can also be done on purpose with other patina chemicals such as bleach, vinegar, salt or ammonia. There are recipes online for anyone who wishes to try. Again, safety measures are important when using these chemicals.
The easiest way to apply varnish to metal is as a spray, in thin layers. It can also be applied in liquid form, with a paintbrush or by dipping, but there’s a higher tendency to create drips that have to be sanded off. The varnish must also be thinned to a very liquid consistency for this method, so it doesn’t accumulate in crevices.
The varnish coating can wear off after some time and may need to be reapplied.
When annealed, copper becomes very soft and malleable. When work hardened it becomes harder than silver or gold, which is why it’s used in those alloys.
It can be soldered with silver solder. The downside is that you get a silver line at the join. Copper plating is used often to hide this solder line. Patina also disguises the difference in colour.
There’s also plumbers copper solder but it doesn’t flow as well as silver solder and it’s also not a perfect match for the copper colour. Plumber’s copper solder is a mix of copper and phosphorus or silver. I do not recommend it for jewellery.
Brass is a metal alloy with a yellow colour made from copper and zinc. Zinc melts at lower temperatures than the other metals mentioned on this page is also used in silver solder, for example.
The yellow tone in brass is colder than gold but just like gold alloys, you can make different tones of brass by varying the quantities of each metal in the alloy.
When brass oxidises it turns brown but when it’s polished it has a very attractive golden yellow color that goes well with copper or silver.
Brass is harder than copper, even after annealing. It can be soldered and forged the same way as copper, silver or gold. Silver solder can also be used with brass.