Printing owes its development first and chiefly to movable metal types. The so-called invention of printing was the discovery of a method of making serviceable type in quantity. The idea of a separate type for each letter of the alphabet was probably conceived long before Gutenberg's time, but it remained for him and his associates to devise an apparatus for making them quickly and accurately enough to be of practical value. That apparatus was the type mold, which experience has since proved to be the most efficient means of securing exactness and uniformity in a number of small pieces of metal.
Type is made of an alloy of lead, tin, and antimony. Its length (technically called height-to-paper) is .918 of an inch. Each type is cast separately in a mold, and has the letter or printing character in bold relief on one end.
Exact uniformity of body is necessary in order that the types, when composed in lines and pages, may be locked together by pressure at the sides so as to make a compact mass. All types in a printing form must be of the same height, so that their faces may present a uniformly level surface from which an impression may be made that will show all the characters clearly. A short type will print faintly or will not print at all, while a long one will be unduly forced into the sheet.
There are on an average about one hundred and fifty roman letters and other characters required in ordinary book printing. These letters are divided into a number of classes: full-body letters, ascending letters, descending letters, short letters; and in some cases, small capitals, which are larger than short letters but not so tall as capitals or ascenders. Only a few letters, like J and Q, cover nearly the entire surface on the end of the type; other letters, like B h l i, cover the upper portion chiefly and leave a blank space at the bottom; while the small letters, like a e o u v, occupy only the middle portion of the surface; still others, like g y p, cover the middle and lower portions of the surface. As all these irregular shapes must be made to appear in line with each other, the type-body on which they are made is larger than the letter. The blank parts around the face of a letter are called the counter, the shoulder, and the beard. The counter is the shallow place between the lines of the face. The shoulder is the low flat part of the type around the face. The beard is the sloping part between the face and the shoulder.
