Alloy was used by the Inuit people. Native copper, however, was found worldwide, along with silver, gold, and platinum, which were also used to make tools, jewelry, and other objects since Neolithic times. Copper was the hardest of these metals, and the most widely distributed. It became one of the most important metals to the ancients. Eventually, humans learned to smelt metals such as copper and tin from ore, and, around 2500 BC, began alloying the two metals to form bronze, which was much harder than its ingredients. Tin was rare, however, being found mostly in Great Britain. In the Middle
Zinc–copper couple greater than 90%, although an alloy containing similar proportions of zinc and copper is used in some cases. The couple is frequently prepared as a darkly-colored powder and is slurried in an ethereal solvent prior to being used in slight excess relative to the substrate. Activation of zinc by copper is essential to the couple’s utility, but the origin of this effect is poorly documented. It is speculated that copper enhances reactivity of zinc at the surface of the alloy. Zinc–copper couple has been prepared by numerous methods, which vary mainly with respect to the source of copper, but also