How could a keyboard cast a whole line of metal letters?

A Linotype machine joined a keyboard to a miniature metal foundry. Instead of printing letters directly, it produced a solid line of raised type called a slug, ready to be arranged with other lines in a printing form.

Pressing a key released a small matrix carrying the recessed shape of a character. Matrices gathered into a line, with special spacing pieces between words. Once the line was ready, the machine positioned it against a mold.

Molten type metal entered the mold and filled the character recesses. After solidifying, the slug carried raised, reversed letterforms along its edge. Ink on that surface could later transfer readable letters to paper. The keyboard had selected the mold shapes, not struck the page.

The matrices could be sorted back into their storage magazine and used again. That reuse separated two jobs: the matrices stored character shapes, while the cast slugs became the material arranged for printing.

A line of text passed through several forms: a sequence of choices, a row of cavities, then a metal relief. This machine made language into a repeatable manufacturing process while keeping the reusable pattern separate from each new copy.