An Overview of Common Alloys and Metals Used in Jewelry

Fine jewelry is created from precious metals, or more commonly, mixtures of metals known as alloys. This article provides some important information about gold, white gold, rose gold, platinum, and rhodium plating. Many different alloys exist today and new ones are developed from time to time, each having different properties. And fine jewelry designers have individual preferences depending on the nature of their work. Here is an overview the alloys you are most likely to encounter today and the important characteristics of each.

Gold has been traditionally popular because of its rich yellow color and because it is very malleable and can be worked into almost any shape. Pure Gold (24 karat gold) is actually too soft for most jewelry applications so it is normally mixed with other metals in various combinations to give it hardness and/or to change its color. Gold purity is expressed in relation to 24 units or karats. 18K is 18/24 or 75% pure yellow gold, 14K is 14/24 or approximately 58% pure yellow gold. Most gold jewelry in the market today is either 14K or 18K, although other levels of fineness such as 10K and 22K are also commonly used.

White Gold is popular for its appearance and price point compared to platinum alloys. Technically there is no such thing as 'white gold', but pure gold can be mixed together with white metals resulting in a whitish alloy. Generally white gold items are electro-plated with Rhodium in the finish stages of production to give them a bright white luster. Rhodium is a member of the platinum family of metals and is the whitest precious metal after silver. Rhodium plating also acts as a hard ‘skin’ that provides additional scratch resistance.

Over time plating may wear off in places. Re-plating is a normally a fairly simple process and is routinely done anytime the piece is repaired or re-polished. Depending on the conditions in which it is worn and the body chemistry of the wearer, the need for re-plating may be more or less frequent.

A popular option for fine jewelry is 18K gold, which is 75% pure gold. It has much of the richness of 24K gold that some of the less pure gold alloys may not. It also has slightly greater density than alloys of lower purity, giving it a more solid feel.

The conventions used to identify the fineness of gold vary to some extent depending on country of origin. In the United States the stamping of fine jewelry is governed by the Federal Trade Commission (FTC).

18K gold is the most recognized global standard and will be usually marked '18K' in the USA and '750' in Europe (750 parts per thousand or 75%).

75% Gold, alloyed with Copper, Silver, Zinc and/or Cobalt

• Rich look and feel
• Does not require plating
• Very workable
• Rarely causes skin irritation

• Slightly less scratch resistant than lower purity alloys
• Will wear down, but over a long period of time and heavy wear

75% Gold, alloyed with Copper, Nickel, Zinc and/or Palladium

• Whitish metal, looks like platinum when plated with rhodium
• Better resistance to bending and scratching than 18K yellow
• Good density, solid feel
• Very workable

• Requires rhodium plating for bright white luster
• Can cause skin irritation for people with nickel allergies
• Will wear down over a long period of time

75% Gold, 25% Palladium

• Whitish metal, looks like platinum when rhodium plated
• Rarely, if ever, causes skin irritation
• Very workable
• Good density, solid feel

• Requires rhodium plating
• Will wear down over a long period of time
• More expensive than 18K nickel alloy

14K gold is a mix of approximately 58% pure gold with 42% other metals such as nickel, copper, silver, and zinc. It is generally identified by the ‘14K’ stamp.

The following are examples of popular 14K alloys. The specific composition of the secondary metals varies:

58.5% gold, 33% copper, 5.5% silver, 3% zinc

• Does not require plating
• Good resistance to scratching and bending
• Will usually not cause skin irritation
• Less expensive than 18K or platinum alloys

• Slightly lighter feel than 18k
• Less ductile than 18K yellow and therefore harder to work with
• Not as resistant to wear as 18k

58.5% gold, 24% copper, 9% zinc, 9% nickel

• Looks like platinum when plated with rhodium
• Good resistance to scratching and bending
• Less expensive than 18k alloys

• Requires plating
• Lighter feel than 18k
• Not as resistant to wear as 18k
• Can cause skin irritation in those who have nickel allergies

According to the FTC guidelines for the jewelry industry, if a manufacturer stamps the purity on a piece of jewelry, it also must stamp their registered hallmark in close proximity as an identifier of the company making the purity claim. This accountability requirement is sometimes violated in the market and you will see jewelry with purity stamps but no company hallmark.

Rose gold, also referred to as pink gold, is experiencing a resurgence in the market. It was popular in earlier times and many fine examples are seen in vintage jewelry. Like other colors, rose gold requires a combination of other metals in the alloy, deriving its reddish tone from copper. Silver and sometimes zinc are also used in to provide additional strength and to attenuate the color.

75% gold, 25% copper and silver

58.5% gold, 41.5% copper and silver

Platinum is a versatile, eternal metal. It is naturally white and does not fade or tarnish. It is ideal for those with sensitive skin because it is hypoallergenic. It is the safest metal for durably setting any kind of gemstone.

Platinum is very dense and malleable, giving it a unique quality. When platinum is scratched very little of the volume is lost; most of the metal is merely displaced and can be re-polished with relatively little loss of metal. As platinum is worn it develops a patina – a subtle texture caused by tiny scratches. Many people like this look, akin to a pair of broken in jeans. It can be always be polished to return the bright shine, and can be polished multiple times without noticeably wearing down. Other metals lose more material over time. Gold prongs wear out and become brittle, and gold rings get thinner with wear. Platinum prongs will bend, but rarely break, and are excellent at resisting wear. This is why the somewhat counter-intuitive statement is true – platinum is softer yet more durable than gold alloys.

There are 4 platinum alloys commonly used in the USA.

Pt900/Ir = 900 parts platinum, 100 parts Iridium

Pt950/Ir = 950 parts platinum, 50 parts Iridium

Pt950/Ru = 950 parts platinum, 50 parts Ruthenium

Pt950/Co = 950 parts platinum, 50 parts Cobalt

95% platinum is the traditional standard, usually marked ‘950Pt’ or simply PLAT

90% platinum is a popular alloy, usually marked 900Pt

50%-90% platinum may be marked ‘PLAT’ in other countries, but in the USA only 950 platinum can be marked simply “PLAT” without the purity indicator.

*Alloys containing less than 50% platinum cannot be marked as platinum according to the FTC guidelines.

Pt900/Ir (900 parts platinum, 100 parts Iridium) is a good hard alloy. A great compromise between relative hardness for ease of polish, excellent white color, and good malleability. It is excellent for both casting and handmade work. Less pressure is required to set gemstones than with harder alloys. It is resistant to scratching & bending and over time is very resistant to signs of wear.

Pt950/Ir (950 parts platinum, 50 parts Iridium) is a good medium-hard alloy which is malleable and the most popular platinum alloy. It’s also the whitest and softest. Good for casting and excellent for handmade pieces, it is the best choice for soft or fragile gem setting. The greater softness requires a longer polishing process. It is less scratch and bend resistant than harder alloys but holds a stone better if an impact occurs; like a shock absorber. Over time it is very resistant to wear.

Pt950/Ru (950 parts platinum, 50 parts Ruthenium) is very hard. It has the highest melting temperature of all platinum alloys and is difficult to cast. Darker gray in color than platinum-iridium, it is less malleable, hard to solder and weld and hard to burnish. Bench workers find it tough on burs, files and drills. Some setters recommend it for diamonds only, since more pressure must be imposed on gemstones during the setting process. It is very resistant to scratching and bending, and thus resistant to signs of wear over time.

Pt950/Co (950 parts platinum, 50 parts Cobalt) is moderately hard. With the lowest flow point of these alloys it is good for even, dense castings of finely detailed pieces including filigree, but not as good for work by hand. Unlike other platinum alloys, this one tarnishes when heated so it needs flux and pickling after soldering just like gold. Since Cobalt is a ferrous metal, not from the platinum group, its scraps must be kept separate from other platinum scraps. It takes a fast polish but finishes darker gray than iridium alloys. It requires moderate pressure on gemstones during the setting process. Bench workers find it more "gold-like" and easy on the tools. It wears quite well over time.

The way the piece is crafted, the heat treatments, welding and soldering applied, and the overall skill of the craftsman are all as critical to the final product as the alloy itself. Seasoned craftsmen and smiths may develop a personal favorite based on experience but no platinum alloy is necessarily "better" or "worse" than others.

Platinum is a wonderful choice of metal for jewelry that is durable enough for a lifetime of wear, and suitable to pass down to future generations as well. As with anything of high economic and sentimental value, the proper care and cleaning of fine jewelry is very important.

In discussions about precious metals people often confuse hardness with strength, but they are not exactly the same.

Hardness = HV

Often referred to as "scratch resistance," hardness is measured using the Vickers Hardness scale. This tests the hardness of a metal by pushing a pointed object into the surface with a specified load and gauging penetration.

Durability = PSI

Tensile strength, a measure of overall durability, is the amount of pressure necessary to break the metal and is measured in pounds per square inch.

Comparisons

18K Gold = 125 HV…29,000 PSI

Pt900/Ir = 110HV…55,000 PSI

Pt950/Ir = 80HV…40,000 PSI

Pt950/Ru = 130HV…66,000 PSI

Pt950/Co = 135HV…64,000 PSI

Gold alloys are generally harder than platinum alloys and will resist scratches better. But Platinum is almost twice as durable as gold, and is more ductile. Platinum therefore can be worked into more intricate forms and has much greater longevity.

Palladium (Pd) is a platinum group metal that has enjoyed inconsistent popularity. It is naturally white and does not require plating as white gold alloys do. It is lighter and less expensive than platinum. When gold and platinum prices are very high, palladium becomes a more popular alternative.

950 Palladium is similar to platinum alloys; 95% palladium with 5% ruthenium by weight.

• Looks similar to platinum
• Does not require plating
• Less expensive than most platinum or gold alloys

• Very lightweight feel
• Darker tone than platinum or white gold
• Difficult to cast and to work with

There are many other specific alloys used in jewelry making to achieve one or another objectives. Creative mixes or treatments can create “fancy colors” such as green, purple and black gold. New alloys are regularly experimented with and sometimes brought to market. As with jewelry styles themselves, the variety of offerings and options available to the consumer in precious metals and alloys reflects a wide variety of preferences and tastes.