Many people associate the metal gold with the color gold. But, some gold jewelry is not golden at all: it’s white.

　　Golden Color

　　Gold is one of the heaviest and softest metals. Pure gold, called 24-carat gold, is so soft that it can be easily dented. In the movies, old-time prospectors bite on yellow nuggets to see if they’re real gold because 24-carat gold will show a bite mark. In the real world, jewelers don’t want to use metal that can be dented so easily. So, most jewelry is actually an alloy of gold with harder metals.

　　Since pure gold is called 24-carat gold, an alloy of half gold and half other metals is called 12 carat gold, because, well, 12 is half of 24.

　　Alloys

　　If most gold jewelry is an alloy, why is some white and some yellow? The final appearance depends on the type of alloy metal used. Alloys made with white metals like silver, palladium and nickel create white-colored gold. Adding some copper to the alloy will restore the yellow color, but too much copper can turn the gold reddish.

　　The color of gold jewelry doesn’t reveal how much gold is in it — a piece of white gold may have the same number of carats as a piece of yellow gold. But, it has a different alloy metal, and so it has a different color.

　　Unlike white gold, fool’s gold has no gold in it at all. It’s a mineral called iron pyrite. Black gold isn’t gold either, it’s oil. Which is also valuable, but doesn’t look as good on your fiancée’s finger.

　　白金为何是白色的？

　　很多人都认为金子就应该是金色。但一些黄金首饰的颜色并不是金色，而是白色。

　　金色

　　黄金是最重最软的金属之一。纯金，也就是24k金质地非常软，很容易产生凹陷。在电影中，以前的勘探者通常会咬一咬黄金来看看是否是真金，这是因为你在24k金上会发现咬痕。然而，在现实世界中，珠宝商并不希望使用那种易产生凹陷的金属。因此，大多数金属实际上是黄金与其他硬金属铸成的合金。

　　由于纯金被叫做24k金，那么由黄金和其他金属各半铸成的合金就叫做12k金，因为12是24的一半。

　　合金

　　如果大多数黄金首饰是合金的话，为什么有的是白色有的是黄色呢？珠宝最终的颜色还要取决于所使用合金金属的类型。用白色金属，如银、钯和镍制成的合金就是白色的黄金。在合金中融入铜可以恢复成黄色，但是如果加入过多铜就会使黄金变红。

　　黄金首饰的颜色并不能说明含金量。一块白金的含金量可能与一块黄金的含金量相同。但由于黄金里掺有不同的合金金属，因此黄金可以呈现出不同的颜色。

　　与白金不同的是，愚人金不含任何黄金。它其实是一种叫做黄铁矿的物质。黑金也不是黄金，而是石油。黑金同样很值钱，但是戴在你未婚妻手指上可不那么好看。