Although degrees in metallurgy or gemology are not needed to make jewelry, it does help to know the names, characteristics, and terminology associated with the materials you will be working with. This section introduces metals and gems, their terminology, the unique measurements associated with them, some specific tools used for their measurement, and other pertinent information needed for their successful use in making metal jewelry.
There are two unique units of measurement for weighing precious metals: the troy ounce and the pennyweight. The troy ounce (ozt.) is a measure of British imperial weight in which there are 12 ounces per pound, unlike our everyday (avoirdupois) ounce in which there are 16 ounces per pound. The troy ounce is usually the preferred measurement for weighing silver and silver alloys.
The pennyweight is a unit of mass, equal to 1/20th of a troy ounce. It was first used during the Middle Ages and it represented the actual weight and value of a British penny, at the time when coins were made with precious metals. In the American market, you will mostly find pennyweights associated with gold and gold alloys.
As you might expect, the weight of metals is measured on a scale, and it is a good idea to have one for the studio. Digital scales are relatively inexpensive and most are capable of weighing in troy ounces, pennyweights, avoirdupois ounces, and grams.
The most distinctive dimensional unit of measuring metals is the gauge. The Brown & Sharp (B&S) gauge system is a standardized method used to measure the thickness of metal sheet and the diameter of wire. This system uses a specialized tool called a gauge plate.
To use this tool, simply slide the wire or sheet metal into the slots, without forcing it, until you find a snug fit.
Measurement units are 0–36 gauge; the higher the number the thinner the sheet or wire.
The reverse side has the decimal-inch equivalents.
The purity of precious metals is where we find the next unique units of measure. Parts per thousand most commonly designates the purity of silver and silver alloys. For example, pure silver is designated as .999—meaning there are 999 parts silver out of 1,000 total parts, or the silver is 99.9% pure. You will never find metals that are 1,000 parts per 1,000, or 100% pure. The metal purity of all precious metals is designated this way. However, there is one unit of metal purity that is used exclusively for gold: the karat. One karat (k) is equal to 1/24 part fine gold, and pure gold has a purity of 24k, which is the same as 99.9% pure.
Most of the time, you will be buying raw materials in the purity level that you desire. But at times, you may be unsure of metal you have. Some karat golds are virtually impossible to distinguish between, as are most silver alloys. So having a way of testing precious metals, although not necessary, is helpful.
Gold fineness can be measured in a number of ways. Electronic testers are available that use chemicals and electric current to decipher the purity of a gold sample.
There is also a centuries-old system to test for gold purity called touchstone testing. This system uses a small block of slate, called a touchstone; a set of known karat gold samples, called test needles; and various chemical solutions that react to different purities of gold. This system can also test for silver and platinum.
Most metals used in jewelry are nonferrous metals—they contain no iron, posses no magnetic properties, and are resistant to corrosion. A number of metals fit into this category; the most common ones used for jewelry are gold, silver, and copper. Although you might use these metals in their pure form when making some jewelry components, you will mostly be using alloys of these metals.
An alloy is a metal that contains two or more different metals. Examples include sterling silver, brass, and 14 karat gold. Why use alloys over pure metals? The short answer is that when you mix different metals together in varying amounts, you change the properties of the dominant metal. This makes the metal more durable against damage and wear. It can also change the color, which expands design possibilities. And it’s more economical, by allowing you to stretch expensive raw materials. The melting point of metal is also changed in an alloy; this is addressed in the Hot Connections chapter (page 50).
Base metal is a term used in jewelry making to describe metals that are not considered precious metals. Base metals are normally used to make inexpensive jewelry and findings, and are usually plated with alloys of silver or gold. The most common base metals used in jewelry, and the ones that will be discussed in this book, are copper, bronze, nickel silver, and brass.
Copper is the only naturally occurring red colored metal. It is a very reactive metal when exposed to moisture and oxygen. It will turn your skin green and can be poisonous with prolonged contact, so it should never be worn directly on the skin. Copper does, nonetheless, make a great accent metal and, because of its reactive nature, takes a patina very well.
Pure copper
Brass is an alloy of copper and zinc; it has a yellowish gold to yellow red color depending on the amount of each metal in the alloy.
Yellow brass
Bronze is an alloy of copper and tin. It has been used for centuries for everything from weapons to sculpture, and its use in jewelry has recently grown in popularity. It presents a warm brownish red to yellowish brown color, depending on the amount of each metal in the alloy.
Bronze
Nickel silver
Nickel silver, also called German silver, is an alloy composed of copper, nickel, and zinc. Although it is commonly mistaken for sterling silver, it contains absolutely no silver.
Base metals are great for the beginner to start with, and for the more advanced jewelry maker to use when learning new techniques. They are inexpensive and readily available from most suppliers. Take note, however, that the predominant metal in these alloys is copper, so jewelry made with these metals may turn your skin green. Also, some people have allergic reactions to nickel, causing a red itchy rash. For these reasons, base metals should not be worn on the skin for long periods of time. You can seal them with a protective layer of lacquer, but the coating will wear off quickly and need to be applied often.
Precious metal is a term used to describe any of the less common, valuable metals that are used in jewelry; the most common are silver and gold.
Fine silver, 99.9% pure, is the most reflective of all naturally occurring white metals. As strange as it might sound, silver was less abundant and more prized than gold in ancient times. Fine silver is a very soft metal and is typically used for components of jewelry, like bezels for stones. Normally, you will use a silver alloy, such as sterling, for the structural component of your piece.
Sterling silver is a mixture of 92.5% fine silver and 7.5% pure copper. This is the most common silver alloy used in jewelry making. Because of the addition of copper, sterling tarnishes more rapidly than fine silver, but it is vastly more durable. Even though sterling contains 7.5% copper, the dominant metal is silver, so the problems associated with copper and copper alloys are virtually eliminated. With such a small amount of copper, sterling silver is nearly indistinguishable from fine silver in color but is nearly three times as strong and hard.
Pure gold, known as 24-karat gold, is 99.9% pure and is the only naturally occurring yellow metal. Like other metals, gold is usually used for jewelry in alloy form. Most gold alloys used in jewelry range from 22k to 10k in purity and are found in a wide range of colors, including yellow, pink, green, and even purple. The color depends on the metals used and the quantity of each in the alloy. The two most common gold alloys are 14k yellow gold, an alloy of 58% pure gold and 42% varying amounts of pure silver and copper; and 14k white gold, consisting of 58% pure gold and 42% other metals in varying amounts, including copper, zinc, nickel, or palladium—another naturally occurring white metal. Comparing white gold to silver, you can see that white gold is not white but much grayer in color. In general, all the gold alloys are highly resistant to tarnishing, but those that have a lower gold content will tarnish quicker.
Sterling silver
14k white gold
14k yellow gold; notice the difference in color compared to 24k gold.
These are the most common metal and metal alloys used in making metal jewelry, though they are just a fraction of what is available today. Aluminum, steel, titanium, and iron are a sampling of other metals that are popular in contemporary jewelry. Even so, the core of jewelry making begins with gold, silver, and copper, the metals that started it all out thousands of years ago.
If you choose to work in multiple metals, mark the alloy type on the metal with a permanent marker and store them separately; an accordion file works great for this.
Like metals, gems have their own unique units of measure. The most important are those for dimension, weight, and hardness. Cut gemstones are usually measured dimensionally (height, width, and depth) in millimeters. Several tools are available for taking these measurements, but the easiest to use is the digital caliper. Most digital calipers measure in inches and millimeters. For the most part, semiprecious gems and some precious gems are bought and sold using these units of measurement, especially in the United States. Millimeters are also the most common unit of measurement in the construction of jewelry.
You will find two main units of weight associated with diamonds and other high-value gems. These are the carat, not to be confused with karat introduced in the metals section, and the point. One carat is equal to 200 milligrams (mg) and a carat is divided into 100 points, each equaling 2 milligrams. Many people confuse these units of weight with the size of a stone. When comparing two 1-carat round diamonds, they will be close in size. But when comparing a 1-carat round diamond with a 1-carat round sapphire, you will notice a distinct difference. The sapphire is a denser stone, which means more weight in a smaller area, and it will be smaller than the diamond. To weigh gemstones, you will need a scale that can measure in thousandths of a gram. Most gem scales will convert to carats with the push of a button.
The last unit of measurement is the most important to consider when selecting a gemstone for a particular piece of jewelry. The Mohs hardness scale is the most common system for categorizing minerals by their hardness. It is a 1 to 10 scale and is based on the ability of one mineral to scratch another. A diamond has a Mohs hardness of 10, and talc, the softest of all minerals, has a Mohs hardness of 1. Why is this important? Because when you are making jewelry, you want to use a gemstone that will sustain the abuse that piece might experience. This is why you typically see the same eight or ten gemstones used in commercial jewelry. Gemstones like garnet, sapphire, diamond, and topaz are hardy stones that can be used in all types of jewelry. This is not to say that you are limited to using the most common stones; rather, you just need to know what to use and when to use it. A good rule of thumb, which can be bent a bit, is that stones with a Mohs hardness of 2–6 should not be used in rings or bracelets but can be used in pendants, pins, and earrings. However, the lower the gem is on the Mohs scale, the more difficult it is to set. Stones with a Mohs hardness of 7–10 work well for any type of jewelry. This range of hardness includes diamonds, sapphires, garnet, topaz, and citrine among others.
Gemstones can be found in a variety of shapes and cuts, some common and some exotic. And with over 100 different natural and man-made gems for use in jewelry, it would take half of this book to introduce you to all of them. There are a number of great gem guides out there that describe every type of gem in detail, and it is an excellent idea to have one for reference. Information on chemical composition, mythologies, and origins are good to know, but very little of that information is important in making jewelry. Besides the hardness of gemstones, the only other things to consider are the shape and the cut, and the quality of these aspects that are the most important.
Let’s begin with the difference between faceted gems and cabochon gems. A faceted gem is what comes to mind when most of us think about engagement rings. The common faceted gem is normally cut from varieties of transparent gem material. They have small flat cuts called facets around the entire surface that are in a geometric pattern. The top of a faceted stone is called the crown, and the bottom is called the pavilion. But the most important feature is the line that separates the two, called the girdle. This is the area of the stone that, if too thin, can cause the stone to crack when setting it; the illustration below shows these features. When buying faceted gems, save yourself a lot of headaches by paying close attention to the girdle, and avoid any stone with a girdle that has a knife-shape edge. Also look for a stone that is proportionate and cut squarely. More on this will be discussed in the stone setting section (page 120).
Cabochon gems are cut from all gem material, whether transparent or opaque. They make up the bulk of the most interesting and varied gems used in jewelry. A common cabochon’s anatomy is not as complex as that of a faceted stone. It’s composed of a top called the head, which is normally a domed surface; a bottom that can be flat or slightly domed; and, like faceted stones, a girdle that separates the two. When choosing a cabochon cut stone, consider the girdle and the bottom edge of the stone, which should have a slight bevel; if these are sharp angles, the stone could chip or crack when setting.
Although there are several other units of measurement for metals and gemstones—such as density, refractivity, and tensile strength, as well as other features and names associated with metals and gems—these are the most important ones to understand. You will use this knowledge not only in the construction and design of your jewelry but also in buying supplies. And if you plan to sell your jewelry, the gemstone specifications are invaluable in the calculation of price and profit.
The appendix (page 216) features helpful conversion charts of measurements, a list of gems and their Mohs hardness, and other helpful information.
