Items bearing an EPNS marking are made of electroplated nickel silver, an alloy of nickel, copper and zinc covered with a thin layer of pure silver in an electrochemical process. Objects marked EPNS were made after 1840, when the electrochemical process was patented in England. EPNS indicates that the object is not sterling silver, which by law must contain 92.5 percent pure silver.
Manufacturers plate electroplated nickel silver items such as flatware or teapots using electricity, potassium cyanide and two electrodes. The item is placed in the potassium cyanide solution with one electrode attached; the other electrode is connected to a piece of pure silver in another tank of solution. Low voltage is passed through the solution to coat the object in a thin layer of silver via electrolysis. The amount of silver coating is often so thin it is measured in microns, but larger pieces sometimes display the amount as a percentage next to the EPNS mark.
A huge commercial success, electroplated items cost only a fraction of the price of sterling silver. Items bearing the EPNS mark also have very little scrap value. They are often used in hotels and on trains for their durability. While it is easy to dent sterling silver items, electroplated nickel silver is much stronger due to the underlying base metal.
Precisely dating electroplated silver nickel items can be difficult. They are often dated based on their style and the way they are made instead of their particular markings.