Testing metals is a precise and varied process in the ancient world. It's a crucial skill in ensuring fair trade and preventing fraud. There are several ways metals are tested in ancient times.
The Art of Testing Metals
Markets of ancient civilizations are huge, with many merchants trading precious metals like gold and silver. To ensure the metals are genuine and of high quality, traders and buyers develop ingenious methods of testing them.
One common method used by ancient traders is the acid test . By applying acid to the metal, they see its reaction and determine its purity. For example, gold doesn't react to nitric acid, distinguishing it from other metals like lead which dissolves in nitric acid.
The Touchstone Technique
Another method widely employed in antiquity is the touchstone technique. This involved rubbing the metal on a touchstone, leaving a distinct mark based on its purity. Marks are compared to those of known metal samples to determine the quality of the metal being tested.
A technique mentioned in the Leyden & Stockholm Papyri c. 300 AD:
Testing of Gold
"If you wish to test the purity of gold, remelt it and heat it: if it is pure it will keep its color after heating and remain like a piece of money. If it becomes white, it contains silver; if it becomes rougher and harder, some copper and tin; if it blackens and softens, lead."
The Archimedes' Principle
A famous test for verifying purity of gold is based on Archimedes' principle. According to legend, the Greek mathematician Archimedes devises a method to determine if the King's crown is pure gold. By measuring the crown's volume and comparing it to the volume of an equivalent weight of pure gold, he can judge its purity.
From the Leyden Papyrus:
Testing of Silver
"Heat the silver or melt it, as with gold; and if it remains white (and) brilliant, it is pure and not false; if it appears black, it contains some lead; if it appears hard and yellow, it contains some copper."
Through these and other methods, ancient traders and buyers hone their skills in detecting counterfeit metals, and counterfeiters learn the tricks of the trade. Counterfeiting isn't noted as a crime in Europe until the arrest of Alexander the Barber in 5 AD Greece.
Before paper money, counterfeiting is often done by mixing base metals with pure gold or silver. One common method is to trim the edges of a coin, a practice known as "clipping", to gather precious metals used in making fake coins.
An ancient form of counterfeit coin, called a fourrée, involves a base metal core plated with a precious metal to mimic its genuine counterpart.
From the Leyden Papyrus:
For Giving to Objects of Copper the Appearance of Gold
"And neither touch nor rubbing against the touchstone will detect them, but they can serve especially for (manufacturing) a ring of fine appearance. Here is the preparation for this. Gold and lead are ground to a fine powder like flour, 2 parts of lead for 1 of gold, then having mixed, they are incorporated with gum, and one coats the ring with this mixture; then it is heated. One repeats this several times until the object has taken the color. It is difficult to detect, because rubbing gives the mark of a gold object, and the heat consumes the lead but not the gold."
When paper money is first used in China during the 13th century, mulberry tree wood is used in its production. Guards are stationed around mulberry forests to control access to the paper, and counterfeiters face the death penalty.
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