Movable Type - Type-founding

Type-founding

Type-founding as practiced in Europe and the west consists of three stages.

Punchcutting: If the glyph design includes enclosed spaces (counters) then a counterpunch is made. The counter shapes are transferred in relief (cameo) onto the end of a rectangular bar of mild steel using a specialized engraving tool called a graver. The finished counterpunch is hardened by heating and quenching (tempering), or exposure to a cyanide solution (case hardening).

The counterpunch is then struck against the end of a similar rectangular steel bar—the letterpunch—to impress the counter shapes as recessed spaces (intaglio). The outer profile of the glyph is completed by scraping away with a graver the material outside the counter spaces, leaving only the stroke or lines of the glyph. Progress toward the finished design is checked by successive smoke proofs; temporary prints made from a thin coating of carbon deposited on the punch surface by a candle flame. The finished letterpunch is finally hardened to withstand the rigors of reproduction by striking.

One counterpunch and one letterpunch are produced for every letter or glyph making up a complete font.

Matrix: The letterpunch is used to strike a blank die of soft metal to make a negative letter mould, called a matrix.

Casting: The matrix is inserted into the bottom of a device called a hand mould. The mould is clamped shut and molten type metal alloy consisting mostly of lead and tin, with a small amount of antimony for hardening, is poured into a cavity from the top. Antimony has the rare property of expanding as it cools, giving the casting sharp edges. When the type metal has sufficiently cooled, the mould is unlocked and a rectangular block approximately 4 centimeters long, called a sort, is extracted. Excess casting on the end of the sort, called the tang, is later removed to make the sort the precise height required for printing, known as "type height".

The type-height was quite different in different countries, the Monotype Corporation Limited in London UK produced moulds in various heights:

• 0.918 inches : United Kingdom, Canada, USA
• 0.928 inches : France, Germany, Swiss and most other European Countries
• 0.933 inches : Belgium height
• 0.9785 inches : Dutch height

A Dutch printers manual mentions a tiny difference between French and German Height:

• 62.027 points Didot = 23.30 mm = English height
• 62.666 points Didot = 23.55 mm = French height
• 62.685 points Didot = 23.56 mm = German height
• 66.047 points Didot = 24.85 mm = Dutch Height

Tiny differences in type-height will cause quite bold images of characters.