Type casting (typography)

Type casting is a technique for casting the individual letters known as sorts used in hot metal typesetting by pouring molten metal into bronze moulds called matrices.

Although using matrices was a technique known well before his time, Johann Gutenberg adapted their use to a conveniently adjustable hand mould, enabling one to easily and accurately cast identical multiple instances of any character, a process which was to become a cornerstone of his 15th century invention of "secret writing".

The ultimate product of manual typecasting were fonts for letterpress printing, and the process starts with the installation of a matrix with the impression of a particular glyph into the bottom of the hand mould which is adjusted for the width of the body and locked in preparation for casting.

Molten type metal alloy would be carefully poured into a straight-sided vertical cavity at the top of the mould. The type caster would then give the mould a quick shake to aid the flow of type metal into every cavity of the matrix. In practice it was discovered that different glyphs would require different shakes to cast the characters properly.

As the casting cooled down and solidified, the mould would be unlocked and the sort removed, ready for later finishing operations and locked again ready for the next character.

All in all, manual casting was a very long drawn-out process, but was able to produce notably excellent results, as can be verified by examining the typography of Gutenberg's 42 line Bible, purportedly his first printed book.

In 1887, Tolbert Lanston invented the Monotype mechanical typesetting machine. This was a type casting system that produced individual characters, in which a matrix case (see picture) is used for holding all the font's matrices.

In a manner somewhat reminiscent to hand type casting, every time a character is to be cast, the selection mechanism would position the matrix case so that the correct matrix is over the mould, hot metal would be injected, the sort removed and the process repeated until the job is finished.

Although the Linotype (1886) and Intertype (1914) approach to mechanical typesetting produced cast slugs that usually represent the complete line instead of individual characters, it still made use of individual bronze matrices stored in a magazine at the top of the machine, dispensed at a time per keystroke, assembled, sent to the caster where the slug was cast and the matrices re-distributed using a clever V-shaped keying mechanism.

The Ludlow display typecasting system is similar, in that it is also a linecasting process, although all the typesetting operations (matrix assembly and later distribution) are executed manually by a compositor.

Subsequent typesetting technologies made use of glyphs represented as photographic negatives or digital descriptions.