Authored by John Sartin
Starting to work with gold can be intimidating. It's more costly than silver and behaves slightly differently at the bench. Fear not. Working with gold is not really all that different than working with silver. In fact, in some cases, it is much easier to work with and has more desirable characteristics.
This first of a three-part series introduces the terminology used with gold, reviews the characteristics of different gold alloys, and explains how those characteristics differ from those of silver.
If you're going to work with gold, the first thing you need to understand is the karat.
Karat is a unit for measuring the purity of gold and is expressed with the letter K, which follows a numerical value, e.g. 24K. Karat is not to be confused with carat, which is a measurement of mass used to express the weight of gemstones.
The karat system is divided into 24 parts, each equal to about 4.165%. Pure 99.9% gold is expressed as 24K and is too soft to be used for most jewelry items. To be workable for jewelry, gold is mixed with other metals to form alloys; the amount of pure gold in each of these alloys is expressed by its karat value, for example, 18K and 14K.
The percentage of gold in an alloy is written as a fraction in which the number on the bottom is 24. If the top number is also 24, the fraction is 24/24, which is pure gold. A familiar alloy is 14K. As a fraction, this would be 14/24, which can also be expressed as .583, in other words, 58.3% pure gold.
The pennyweight, abbreviated as dwt., is the traditional unit of measurement for gold mill products in the United States; this precise unit of measure allows for more accuracy than troy ounces. There are 20 pennyweights in a troy ounce (ozt.) of gold, and one pennyweight is equal to .05 ozt. or 1.56 grams. When you order gold (and platinum) fabrication metal, Rio Grande will base the price on how many pennyweights of gold are in your order.
A gold alloy is a mixture of pure gold and another metal or metals. Alloying does several things to the properties of gold, including increasing its hardness and tensile strength, changing its color and, in most cases, decreasing its melting temperature.
The metals that are mixed with gold to form an alloy vary but usually include silver and copper. Other metals, such as zinc, nickel and palladium, can be added to achieve a certain result, including increasing flow characteristics or acting as a bleaching agent. When one property of a metal is changed, it will affect the entire alloy. There is always a tradeoff. For example, nickel will bleach gold to form a white metal, but it makes the alloy brittle and difficult to work. Knowing the properties of the gold alloy you are using is crucial to working with gold successfully.
The general properties of gold alloys include hardness, melting point, and tensile strength.
|Alloy||Composition||Melting Point (approx.)||Hardness HV Annealed (approx.)||PSI (approx.)|
|24K gold||99.9% Au||1063°C / 1800°F||20||18,000|
|22K gold||92% Au + 8% Ag, Cu||982°C / 1800°F||52||31,900|
|18K yellow gold||75% Au + 25% Pd, Ag, Cu||1882°C / 1620°F||135||72,500|
|18K nickel white gold||75% Au + 25% Pd, Ag, Cu||910°C / 1670°F||220||103,000|
|18K palladium white gold||75% Au + 25% Pd, Ag, Cu||1020°C / 1868°F||95||60,000|
|14K yellow gold||58.5% Au + 41.5% Ag, Cu||810°C / 1490°F||150||85,500|
|14K nickel white gold||58.5% Au + 41.5% Ag, Ni, Cu||930°C / 1706°F||177||101,200|
|14K palladium white||58.5% Au + 41.5% Pd, Ag||1110°C / 2030°F||82||60,000|
|14K red||58.5% Au + 41.5% Ag, Cu||935°C / 1715°F||160||79,700|
|10K yellow||41.7% Au + 58.3% Ag, Cu||891°C / 1635°F||50||35,500|
|fine silver||99.9% Ag||961°C / 1762°F||22||20,300|
|sterling silver||92.5% Ag + 7.5% Cu||820°C / 1580°F||66||40,000|
Each of these properties is important. Taken as a whole, they will dictate how you work with gold in your designs.
We've included a chart of the most common gold alloys and how they compare to sterling and fine silver. This is a general guideline. Each alloy's characteristics will change slightly depending on the refiner it comes from. Because of this, it is not uncommon to change the way you work with gold when you change suppliers or karat values.
Scanning down the hardness column on the chart, it's clear that alloys significantly change depending on what is added.
For instance, the characteristics of 24K gold are drastically changed with an addition of just 8% other metal. The melting temperature decreases, and the alloy becomes harder and slightly more difficult to form. When comparing 14K gold to 24K gold, the melting temperature is 500°F lower, and the metal is seven times harder and has four times the tensile strength.
The color of gold also changes when it is alloyed. 14K gold is much different in color than 24K because it has less pure gold. Red golds (pink, rose, etc.) have a higher percentage of copper than yellow gold, which shifts the color to a redder hue. If an alloy has higher silver content, the color will shift toward a light green color.
Tthere are two metals commonly used to create white gold alloys: palladium, which is a member of the platinum group of metals, and nickel.
Since white gold is not truly white, most white gold finished jewelry and jewelry components are plated with rhodium, which is another metal of the platinum group. You should take this into account before accepting a repair job on a piece of white gold jewelry because you will most likely need to re-plate the entire piece after the repair.
If you're working with nickel-based white gold, it's important to remember that some people have a nickel allergy. If you're selling your work in Europe, you should be aware of EU regulation EN1811:2011+A1:2015, which governs the levels of nickel allowable in products that have prolonged contact with the skin, including jewelry.
Most oxidation, or tarnish, in precious metal alloys is caused by a reaction between copper and the environment. The higher the percentage of copper in the alloy (whether gold or silver), the more susceptible the metal will be to oxidation.
With most gold alloys, oxidation over time is not noticeable because the yellow oxide color is not as apparent as it is on sterling silver. As with sterling silver, the oxidation of a gold alloy will accelerate if it is exposed to chemicals such as chlorine from swimming pools or hot tubs, household cleaning products, hand lotions and perfumes, as well as the wearer's body chemistry.
Read Part Two for general information and how to successfully work with gold alloys for your jewelry making. Get tips on stone setting and finishing your gold jewelry in the third and final part.