Stamp mill

A stamp mill (or stamp battery) is a type of mill that crushes material by pounding rather than grinding, either for further processing or for extraction of metallic ores. Breaking material down is a type of unit operation.


Stamp mills were used in early paper making for preparing the paper-stuff (pulp), before the invention of the Hollander beater. They were used in mining for breaking ore, and in oil-seed processing for prior to pressing the oil from the milled seeds. Early mills were water powered but mills can be steam, water, or electric powered.

Californian stamps are stamp mills developed for use in the Californian gold mines. They are based on the Cornish stamps but were more rapid in action, and the heads and lifters were made to rotate so that they wore more evenly. The other advantage of the Californian stamp was that a single head could crush 1.5 tons of ore as opposed to the Cornish stamps which could only crush 1 ton.

Cornish stamps are stamp mills developed for use in the Cornish Tin mining operations around 1850. Cornish Stamps are machines used to crush small lumps of ore into sand like material. Constructed from heavy timber or iron lifters with iron “heads” at the bottom were raised by cams on a rotating axle, and fell on the ore and water mixture, fed into a box beneath. The heads normally weighed between 4 and 8 cwt each, and were usually arranged in sets of four, in timber frames. Small stamps were commonly powered by water wheels and larger ones by steam engines.


A stamp mill consists of a set of heavy steel (iron-shod wood in some cases) stamps, loosely held vertically in a frame, in which the stamps can slide up and down. They are lifted by cams on a horizontal rotating shaft. On modern mills, the cam is arranged to lift the stamp from the side, so that it causes the stamp to rotate. This evens the wear on the shoe at the foot of the stamp. As the cam moves from under the stamp, the stamp falls onto the ore below, crushing the rock, and the lifting process is repeated at the next pass of the cam.

Each one frame and stamp set is sometimes called a "battery" or, confusingly, a "stamp" and mills are sometimes categorised by how many stamps they have, i.e. a "10 stamp mill" has 10 sets. They usually are arranged linearly, but when a mill is enlarged, a new line of them may be constructed rather than extending the line. Abandoned mill sites (as documented by industrial archaeologists) will usually have linear rows of foundation sets as their most prominent visible feature as the overall apparatus can exceed 20 feet in height, requiring large foundations. Stamps are usually arranged in sets of five.

Some ore processing applications used large quantities of water so some stamp mills are located near natural or artificial bodies of water. For example, the Redridge Steel Dam was built to supply stamp mills with process water.


Stamp mills were first used by miners in Samarkand from as early as 973. They were used in medieval Persia for the purpose of crushing mineral ores. By the 11th century, stamp mills were in widespread use throughout the medieval Islamic world, from Islamic Spain and North Africa in the west to Central Asia in the east.

The first stamp mills in Europe were in use from the Renaissance period. Numerous water-powered stamp mills are illustrated in book 8 of Georg Agricola's De Re Metallica, published in 1556. The mills Agricola shows were largely wooden construction, excepting the use of iron shoes on the end of each stamp. The camshaft was set directly on the axle of the waterwheel, and stamps were typically arranged in gangs of three, with each wheel driving one or two gangs.

The first stamp mill in the U.S. was built in 1829 at the Capps mine located near Charlotte, North Carolina. They were superseded in the 2nd half of the 19th century in many applications by more efficient methods of processing. However their simplicity meant that they were used in remote areas for ore processing well into the 20th century. (19th century advertisements for some mills highlighted that they could be broken down, packed in by mule in pieces, and assembled on site with only simple tools) They were quite common in gold, silver and copper mining regions of the US in the latter half of the 19th and early 20th centuries, where the ore was crushed as a prelude to extracting the metals.

See also

  • Hammer mill - A more modern device that also can crush material to fines.
  • Ball mill - a horizontal cylinder containing metal balls to crush the material
  • Stamp sand - the product of ore mills


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