Over the centuries, metallurgists and metalsmiths developed different types of gold colored material to meet a variety of needs. A damaged jewelry piece made of pure gold probably inspired one of our metal-loving forebears to experiment. Gold is strengthened by adding a little silver and zinc, for example. Jewelers have adopted a number of golden alloyed metals and developed more affordable layered metals to use for material as well. In this article, we will describe 9 types of gold and golden-hued metals found in jewelry making. It is important for contemporary metalsmiths to understand the strengths and weaknesses of each material choice.
24 karat pure gold
24 karat gold is the element in its purest form. It is a rich, aqueous yellow color. In antiquity, metalsmiths used high karat or pure gold in jewelry for royalty. However, the items are so pliable you can bend them with your fingers and scratch them with your nails. Pure gold is easy to dent and even stretch if the pieces are thin. This fragility is not practical. Today, 24 karat gold (or close to it) is most frequently used for surface applications of plating or thin gold foil sheets, sometimes called gold leaf. Gold foil is bonded to other metals for an ornamental effect, often in feathered, papery designs. One technique from Korea called keum-boo involves bonding gold foil to silver through a heating and burnishing process.
Yellow Gold Alloys
Pure gold is mixed with other metal elements while in the molten state to create alloys with different properties such as strength and various colors. The most common type of gold alloy is yellow in color and contains silver and zinc. The resulting material is more durable for long lasting jewelry that is easy to care for. It also makes the material somewhat less expensive.
The karatage system describes the ratio of pure gold to other metals in the alloys. In the United States, for example, the standard for solid gold jewelry is 14 karat gold. If you apply the ratio 14/24 karats, you can calculate that it is 58.3% pure gold. It is the most common alloy in our country but buyers should note that other alloys are available with lower and higher karatages. Jewelers are required to disclose the karats of the material on finished pieces of jewelry. A quality mark or hallmark is stamped or engraved on the piece with the karatage. Other examples at the low and high end of the market are 10 karat gold (10/24), which is 41.6% pure, and 18 karat gold (18/24), which is 75% pure gold. The karatage of the alloy obviously affects the price points of the finished items. It also affects the color of the metal with higher karat alloys being more yellow and lower karat varieties appearing more muted.
Colored Gold Alloys
Whatever the intensity of the color, we usually think of gold as a yellow toned metal. However, you can get a range of gold karatage in different colors if you vary the added metals in the alloys. White gold contains nickel, for example. The addition of copper to a gold alloy will result in the rose gold that is so trendy today. With a little less copper and a different ratio of silver and zinc, it is possible to alloy green gold.
Copper Based Alloys
Brass & Bronze are both primarily made of copper. These base metals have the highly prized golden tone that is popular in adornment; but, they are made from low-cost metals and frequently used for costume jewelry. Antique jewelry items were often made from bronze. Brass has become more common in modern times. Both are prone to tarnish and may turn the wearer’s skin green. The discoloration is a harmless reaction for most people, but some individuals are allergic to these materials and should avoid them. Polishing copper based alloys will remove tarnish. Or, plating either alloy with other metals will improve the finish and delay tarnish.
Brass is a bright yellow or reddish alloy made up of copper and zinc. There are so many combinations of brass alloys that European Norm Standards have more than 60 types of brass on record. The two specific variations described below are most common for jewelry making. Brass is a low-cost, attractive metal with a golden tone and it is malleable and easy to manipulate so it can be fabricated or cast. Unfortunately, soldering brass creates a visible seam that needs to be covered through design construction or plating for aesthetic reasons.
- Red brass = 15% zinc and 85% copper. The high level of copper in red brass creates the red tone in the alloy.
- Yellow brass = 33% zinc and 67% copper. Yellow brass is bright and shinier than red brass.
Bronze consists of 12% tin (or other metals) and 88% copper. The resulting alloy has a warm, brown tone and is quite brittle. Therefore, bronze items are cast into thick forms to avoid weak points that could break. Fabricating bronze pieces from sheet and wire is not practical. Besides the beautiful golden color of bronze, an interesting fact is that it expands slightly when it goes from a molten state to a solid. Jewelers must plan for this expansion when casting.