英语听力文摘 English Digest 620、白金为何是白色的？

 　　What Makes White Gold White?

　　Many people associate the metal gold with the color gold. But, some gold jewelry¹ 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 dented². In the movies, old-time prospectors³ 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 alloy⁴ 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.

　　Alloys⁵

　　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 copper⁶ 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.

1 jewelry   

n.（jewllery）（总称）珠宝

参考例句：

• The burglars walked off with all my jewelry.夜盗偷走了我的全部珠宝。
• Jewelry and lace are mostly feminine belongings.珠宝和花边多数是女性用品。

2 dented   

v.使产生凹痕( dent的过去式和过去分词 )；损害；伤害；挫伤（信心、名誉等）

参考例句：

• The back of the car was badly dented in the collision. 汽车尾部被撞后严重凹陷。
• I'm afraid I've dented the car. 恐怕我把车子撞瘪了一些。 来自《简明英汉词典》

3 prospectors   

n.勘探者，探矿者( prospector的名词复数 )

参考例句：

• The prospectors have discovered such minerals as calcite,quartz and asbestos here. 探矿人员在这里发现了方解石、石英、石棉等矿藏。 来自《简明英汉词典》
• The prospectors have discovered many minerals here. 探矿人员在这里发现了许多矿藏。 来自辞典例句

4 alloy   

n.合金，(金属的)成色

参考例句：

• The company produces titanium alloy.该公司生产钛合金。
• Bronze is an alloy of copper and tin.青铜是铜和锡的合金。

5 alloys   

n.合金( alloy的名词复数 )

参考例句：

• This is essentially a development of thoria dispersion strengthened nickel alloys. 这基本上是用二氧化钍弥散强度化的镍基合金。 来自辞典例句
• The lack of deep hardening in these alloys negates their use. 这些合金缺乏深层硬化能力使它们无法利用。 来自辞典例句

6 copper   

n.铜；铜币；铜器；adj.铜(制)的；(紫)铜色的

参考例句：

• The students are asked to prove the purity of copper.要求学生们检验铜的纯度。
• Copper is a good medium for the conduction of heat and electricity.铜是热和电的良导体。