In 1876 a German inventor named Ottmar Mergenthaler demonstrated his linotype machine to the "New York Tribune's" editor, Whitelaw Reid. The "New York Tribune" adopted the linotype first, and the machine proved itself to be one of the most important letterpress inventions since Johannes Gutenberg's initial movable-type printing press.
The linotype machine, by quickly assembling type and producing type slugs with less work on the part of its human operators, made possible the multi-editioned newspapers as well as the numbers of books and magazines that characterized the 20th century.
Most newspaper publishers retired the linotype machine in the 1970s and 1980s and replaced it with faster computerized systems.
Linotype machines have four major components: magazine, keyboard, casting mechanism and distribution mechanism.
The operator sits in front of the keyboard and below the copy. By pressing a button on the 90-character keyboard, the operator activates a mechanism that releases the letter mold from the magazine that hold and organizes the matrices. The matrices travel through conveyor belts from the magazine into the assembler box in front of the operator.
Once the operator has a series of matrices in a single line of text, he raises a small lever that sends the assembled line to the machine's casting mechanisms. At this point the operator's job with that line is over and he begins setting type for the next line.
When the operator raises the casting lever, the machine moves the assembled line to the casting section and automatically performs the series of steps to produce the slug.
The machine moves a mold wheel forward and the line of matrices forms a metal-tight joint over an opening in the wheel. The linotype machine then pours molten metal over the matrices and casts a line of text.
The mold wheel revolves after casting the slug, and turns the slug from the horizontal casting position to a vertical position, trims the base and ejects the finished slug for printing use.
The use of molten type metal is why printers call this process "hot metal typesetting."
After casting, the machine must send each matrix and spaceband back to specific boxes containing those characters for reuse as molds.
To do so, the linotype machine takes the assembled matrices upwards until the teeth along the bottom of each matrix catch on to a carrier bar mechanism. The carrier bar takes the matrices to the distributing mechanism and drops the spacebands, which fall back into the spaceband box of the magazine.
The machine carries the matrices along a seven-ribbed steel distributor bar over the channels for each character (letters, numbers and punctuation marks). Each character has a different set of ridges, which tell the machine when to drop the characters into their correct places in the magazine, ready again for use.
Due to the speed of the linotype machine and the complexity of its operations, oil cannot be allowed near the matrix path. Typesetters instead lubricate the channels for matrices with graphite.
When the matrix path becomes oily, due to sloppy maintenance or from the oil used on other parts of the linotype machine, the oil mixes with the graphite and dust to produce a gummy substance. The resulting stickiness in the magazine means that the matrixes will not travel from the magazine at their usual speed and may enter the assembly box out of sequence. The letters will appear out of order, which typesetters call a "matrix transposition."