Gold is most well-known for its bright, shiny, yellow color. However, pure gold can also appear in other colors when it is alloyed with other metals. So in some cases, gold can take on a darker color ranging from pale yellow to black. The color of gold depends on the type and amount of metals it is mixed with. Let’s take a closer look at how alloying changes the color of gold.
Pure Gold
Pure gold is called 24 karat gold. It contains 99.9% pure gold with no other metals mixed in. 24 karat gold has a bright yellow color because of how the electrons in the gold atoms interact with light. The specific wavelengths of light that gold absorbs and reflects back determine its yellow color.
So in its purest form, gold does not come in a dark color. It maintains that familiar glowing yellow look we commonly associate with gold jewelry, coins, and bars. If you have a gold item that is a dark color, it is likely an alloy containing gold, not pure gold.
Alloying Gold with Silver
One way to transform gold into a darker color is to alloy it with silver. When gold is mixed with silver, it takes on a pale yellow or “green” gold color. The more silver content in the alloy, the paler the gold becomes.
Here are some examples of gold-silver alloys:
| Alloy | Gold Content | Silver Content | Color |
|---|---|---|---|
| 22 karat | 91.6% | 8.4% | Pale yellow |
| 18 karat | 75% | 25% | Pale yellow |
| 14 karat | 58% | 42% | Light green-yellow |
| 10 karat | 41.6% | 58.4% | Green-yellow |
As you can see, increasing the silver content causes the gold to transition from a pale yellow to a light green-yellow color. 14 karat and 10 karat gold alloyed with high amounts of silver take on a distinctly darker green-yellow tone.
Alloying Gold with Copper
Another way to create a darker gold color is to mix gold with copper. Copper provides a reddish tone that combines with gold’s yellow to produce a deeper, warmer color.
Some common gold-copper alloys include:
| Alloy | Gold Content | Copper Content | Color |
|---|---|---|---|
| 18 karat | 75% | 25% | Deep yellow |
| 14 karat | 58% | 42% | Rich yellow |
| 10 karat | 41.6% | 58.4% | Orangey yellow |
The higher the copper content, the more orange and red tones come through in the gold. 10 karat gold with over 50% copper has a distinctive orangey-yellow color.
Alloying Gold with Nickel and Zinc
Nickel and zinc are also used in some gold alloys to create a white gold color. White gold contains a minimum of 58% gold, combined with nickel, zinc, and sometimes silver or palladium.
Nickel gives white gold a soft platinum-like appearance. However, some people have nickel allergies and cannot wear jewelry made from nickel alloys.
Palladium and zinc are hypoallergenic alternatives for white gold alloys. These metals maintain the white color but are less likely to cause skin reactions.
Alloying Gold with Manganese and Iron
Manganese bronze and iron are sometimes added to gold jewelry alloys in very small amounts. These metals help increase the hardness and durability of gold for use in rings, bracelets, and other wearable pieces.
The manganese gives the gold a deeper yellow color while the iron appears more grayish. But because these metals are only used in tiny percentages, they don’t drastically change the overall look of the gold.
Alloying Gold with Cadmium
Cadmium forms deep yellow gold alloys when combined with gold. Jewelry will sometimes contain around 13% cadmium to enhance the yellow tones.
However, cadmium is toxic so these gold alloys are rarely used in modern jewelry. Cadmium exposure can cause health issues so many governments have restricted the amount allowed in jewelry.
Oxidization Effects
The color of gold can also darken if the surface oxidizes. When gold is exposed to air and chemicals over a long period of time, it may develop a thin layer of oxidization. This oxidized layer can range from pale yellow, to brown, to nearly black depending on the thickness.
So old gold coins or artifacts that have oxidized will appear several shades darker than they originally were. Gently polishing the surface can help remove this layer and reveal the actual gold color underneath.
Conclusion
While pure gold is only available in a bright, radiant yellow, alloying gold with other metals can alter its color. Silver, copper, nickel, zinc, manganese, iron, and cadmium can combine with gold to produce darker colors including pale yellow, green-yellow, reddish yellow, white gold, and deep yellow shades. Oxidization over many years can also cause gold surfaces to turn brown or black.
So in summary, the answer is yes – gold can be a variety of dark colors when it is alloyed with certain metals or allowed to oxidize over time. The carat, alloy recipe, oxidation levels, and polishing of the surface all contribute to the final color you see.
