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An alloy with only gold and silver is the hardest at 15.5 K (64.5% gold and 35.5% silver). During ancient times, due to impurities in the smelting process, gold frequently turned a reddish color. This is why many Greek and Roman texts, and some texts from the Middle Ages, describe gold as "red".
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A superhard material is not necessarily "supertough". For example, the fracture toughness of diamond is about 7–10 MPa·m 1/2, [16] [17] which is high compared to other gemstones and ceramic materials, but poor compared to many metals and alloys – common steels and aluminium alloys have the toughness values at least 5 times higher. [18]
This is a list of named alloys grouped alphabetically by the metal with the highest percentage. Within these headings, the alloys are also grouped alphabetically. Within these headings, the alloys are also grouped alphabetically.
Diamond (Mohs 10) is 1500 (off scale). Diamond was the hardest known naturally occurring mineral when the scale was designed, and defines the top of the scale, arbitrarily set at 10. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, or the softest material that can ...
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Shakudō (赤銅) is a Japanese billon of gold and copper (typically 4–10% gold, 96–90% copper), one of the irogane class of colored metals, which can be treated to develop a black, or sometimes indigo, patina, resembling lacquer.
Its color ranges from black to brown and gold, depending on the chemical bond. It is one of the hardest known materials, along with various forms of diamond and other kinds of boron nitride. Borazon is a crystal created by heating equal quantities of boron and nitrogen at temperatures greater than 1800 °C (3300 °F) at 7 GPa (1 million lbf/in 2 ).