Matrix case for use in a Monotype composition caster.

The case is full of matrices of letters, figures, and punctuation for one typeface design and one size. This example has 16 x 17 rows giving 272 possibilities, which allows roman, italic and bold variants to be grouped together. A case with 15 x 17 rows holding 255 matrices was much more common. Prior to 1924 it held 15 x 15 rows. Monotype typefaces were designed on an 18-unit to the em system, the narrowest (e.g. comma, full stop, or lowercase ‘i’) being 5 units wide and the widest (e.g. capital ‘W’) being 18. In the Monotype system, the width of an em – known as set-width – varied from typeface to typeface and from size to size. All the characters in any horizontal row had to be the same unit width.

Operation of the Monotype keyboard resulted in holes being punched in a paper ribbon that was taken to the caster when complete. As the ribbon was fed through, the matrix case sitting within the casting machine moved into position and single pieces of metal type were cast letter by letter.