Matrix (printing)

In the manufacture of metal type used in letterpress printing, a matrix (from the Latin meaning womb or a female breeding animal) is the mould used to cast a letter, known as a sort. Matrices for printing types were made of copper. However, in printmaking the matrix is whatever is used, with ink, to hold the image that makes up the print, whether a plate in etching and engraving or a woodblock in woodcut. In letterpress or "cold metal" typesetting, used from the beginning of printing to the late nineteenth century, the matrix of one letter is inserted into the bottom of an adjustable-width hand mould, the mould is locked and molten type metal is poured into a straight-sided vertical cavity above the matrix. When the metal has cooled and solidified the mould is unlocked and the newly cast metal sort is removed. The matrix can then be reused to produce more copies of the sort. The sorts could then be cleaned up and sent to the printer. In a low-pressure hand mould matrices are long-lasting and so could be used many times. In the hot metal typesetting systems of the later years of metal type printing, from the late nineteenth century onwards, new type is cast for each job under the control of a keyboard. The matrix or mats for a complete font are loaded into a matrix-case and inserted into a casting machine, which casts the required sorts (or, in a Linotype machine, a solid block for each line) for a page composition automatically, often from a paper reel. The standard method to make a matrix was to drive a steel punch in the shape of the type to be made into soft copper. The matrix could then be cleaned up and cut down to the width of the letter to be cast: this is called "justification" and sets the width of the letter when cast. An matrix that has not yet been justified is called a "strike". Adjustment of the matrix had to be done very carefully to ensure even flow of letters on the page. Large typefaces, or wide designs such as emblems or medallions, were never very easily produced by punching since it was hard to drive large punches evenly.