The denominations of the coins once determined, the size, weight, and substance are dictated chiefly by convenience, and in this respect the different systems exhibit remarkable similarity. In the countries with the small units the smallest coin and those representing two, five, ten, and twenty times its value are made of cheap metals, such as copper, bronze, or nickel; those representing half the value of the unit or fifty times the value of the smallest coin, the unit, and its multiples up to five, are made of silver, and the coins of higher denominations of gold. In other countries coins of corresponding value are made of the same metals. In the United States, for example, the one- and two-cent pieces are copper, the five-cent piece nickel, the ten-, twenty-five-, and fifty-cent pieces and the dollar coins are silver and the others gold. In England the penny, half-penny, and farthings are bronze, the sixpence, shilling, two-, two-and-a-half-, and five-shilling pieces silver, and the coins of higher denominations gold. In Germany the one- and two-pfennig pieces are copper, the five- and ten-pfennig pieces nickel, the twenty- and fifty-pfennig, one-, two-, and five-mark pieces are silver and the other coins gold. In France the five- and ten-centime pieces are copper, the fifty-centime, one-, two-, and five-franc pieces silver, and the coins of higher denominations gold. Indeed, as nearly as the size of their respective units will permit, the coins of the various nations correspond to each other in size, weight, and substance, a fact which clearly shows the universal dominance of commercial interests in monetary matters. Despite the fact that the manufacture of coins is a government monopoly the world over, and despite the differences in the history, political characteristics, and economic and social policies of the different nations, common commercial needs have given to their coinage systems the same general features.

In order to render gold and silver coins more durable and thus to protect them as much as possible from loss by abrasion, the pure metal is usually mixed with copper or, in the case of the gold coins, sometimes with a mixture of copper and silver. This admixture is known as alloy, and the metal thus hardened is known as standard gold or standard silver to distinguish it from the pure metal. The most common practice at the present time is to use nine parts of pure gold or silver to one part of alloy, and the coins manufactured from metal of this standard are said to be nine-tenths fine. The process of increasing largely the proportion of alloy to pure metal is called debasement, a practice which, as we have previously noted, was very common in the Middle Ages and was one of the reasons for making coinage a government monopoly and for surrounding it with all possible safeguards.