In printing and typography, hot metal typesetting (also called mechanical typesetting, hot lead typesetting, hot metal, and hot type) is a technology for typesetting text in letterpress printing. This method injects molten type metal into a mold that has the shape of one or more glyphs. The resulting sorts or slugs are later used to press ink onto paper. Normally the typecasting machine would be controlled by a keyboard or by a paper tape.
It was the standard technology used for mass-market printing from the late nineteenth century until the arrival of phototypesetting (also called cold type) and then electronic processes in the 1950s to 1980s.
History Hot metal typesetting was developed in the late nineteenth century as a development of conventional cast metal type. The technology had several advantages: it reduced labour since type sorts did not need to be slotted into position manually, and each casting created crisp new type for each printing job. In the case of Linotype machines, each line was cast as a robust continuous block (hence "line o'type") which was useful for rapid newspaper printing.
Types of typesetting Two different approaches to mechanising typesetting were independently developed in the late 19th century. One, known as the Monotype composition caster system, produced texts with the aid of perforated paper-ribbons. Each character was cast separately. These machines could also produce texts in "large-composition" up to 24 point.
The Super-caster, another machine produced by Monotype, was similar in function to the Thompson, Barth, pivotal and other casters but designed to produce single type (including even larger sizes) for hand setting.
The other approach was to cast complete lines as one slug, usually comprising a whole line of text.
Of this system there were at least five manufacturers:
Linotype Intertype Corporation the Typograph, produced in Germany Ludlow Typograph The Monoline, a very basic machine
The Linotype and similar Intertype machines came out with paper tape and electronic automation near the end of their lifecycles, which allowed for the news wire services to send breaking news to remote newspaper offices for prompt setting into late editions.
While the other machines were operated by (non-QWERTY) keyboards, in the Ludlow Typograph the matrices for each line were assembled in a stick by hand. This machine was able to cast display body sizes that other mechanical composition systems were unable to produce. In this way headings could be produced to complement text produced on other machines. It also used the same alloy as Linotype machines, so was a useful adjunct to page makeup for newspapers as, when a print run was completed, all the metal could be remelted at once, without having to be separated or the type from the headings redistributed back into case.
The success of these machines lay in different fields. The Monotype caster was more popular for bookwork that required the ability to make manual corrections and edits while the slug casting systems found success in newspaper production, where speed of production and 'make ready' for print was essential.
Another essential difference between Monotype and the "slug"-producing machines is that a Monotype machine functions with a minimal set of matrices. Each character needs one matrix. Linecasters cannot function this way, and these systems need quite large magazines of matrices to be able to set a complete line of text with the usual character repetitions. Indeed, the nominal 90-channel magazine of a linecaster really has 91 total channels, with the first two channels allocated to the lower case 'e', and with these matrices being alternately selected from channel 0 or channel 1, for alternate lines of cast type.
Additionally, Monotype must use a punched paper tape, and the "reading frame" is always backwards (right-to-left) in order to achieve justification, as justification is not an inherent capability of the machine (however, "flush left" is an inherent capability). Whereas Linotype may use a punched paper tape, although this option is seldom-used outside of daily newspapers, and whether a tape is used, or not, the "reading frame" is always forwards (left-to-right), with justification being an inherent capability of the machine (and, "flush right", "centered" and "flush left" may be very easily accommodated manually, or automatically using a "quadder" attachment).
Linotype
The key feature of the Linotype is the use of molds which circulate through the machine in its various stages of operation. One type is a space band (a special two-part sliding wedge) and the other is a letter matrix made of brass. The matrices are stored in one or more magazines on top of the machine (providing the operator with a choice of fonts; these can also be exchanged with other extra magazines as desired) while the space bands are stored in a box closer to the keyboard.
Once a key is pressed, the matrix passes through what is known as the ‘assembler front’, down past a rotating fiber reinforced wheel (known as the star wheel) and into the ‘assembling elevator’ which serves the same purpose as the hand compositor's stick. When the space band key near the keyboard is pressed, one of the space bands drops out of the box and almost directly into the assembling elevator. The assembling elevator (or more commonly just the ‘assembler’) is adjustable for different lengths of line (in picas).
Once the line approaches its correct length, the operator is made aware of this by a bell or other indicator. If the line is ‘loose’ or too short, there is too much ‘white space’ for the space band wedges to fill out the line, and the matrices could possibly turn sidewise or fail to seal against each other as the machine prepares for the casting operation. If the line is ‘tight’ or too long, the elevator carrying the matrices and space bands will not seat properly in front of the mold slot. Both the Linotype and Intertype machines have two important safeties that act during the casting operation – the ‘pump stop’, which comes into play on loose lines, and the ‘vise automatic', which comes into play on tight lines. Both scenarios, if not stopped by these safety features, usually result in a “squirt” of molten type metal, encasing the matrices and the elevator in metal in the process. Not only is it time-consuming to clean up after a squirt, a tight line usually has not come down far enough to mate with the slots on the mold face, resulting in damage to the matrices. Therefore, it is considered very poor form for an operator (or the machinist who cared for the machine) to permit this to happen.
When the line is assembled to the correct length, the operator presses down on a lever which raises the assembling elevator up into the delivery channel and starts the automatic casting cycle. The delivery channel transfers the matrices out of the assembler and into the first elevator. The first elevator then descends to a position in front of the mold, and if the elevator has not descended fully by the time the machine starts the process of aligning the matrices (most often caused by a ‘tight’ line), the first of the two safeties, the vise automatic, brings the machine to a full stop before the supporting lugs on the matrices are crushed by the mold. Once the matrices are in proper position, two actions take place in sequence: the matrices are aligned vertically and face-wise while a bar rises from below to force the movable sleeves on the space bands upwards to cause them to fill out the line to the exact width of the mold. If the justification bar has made a full cycle and the line is still not fully justified, the second safety, the pump stop, prevents the plunger in the metal pot from going down. The space bands were an important feature of this machine, providing automatic justification of each line by equally adjusting the white space between each word. Since the type used was proportional and not fixed in width, solving this justification problem mechanically was very important. Some later models had a feature that permitted the lines to be cast with the alignment to either left, right or centered. Operators running earlier models would use special ‘blank’ matrices (in four sizes) to manually create the proper amount of whitespace beyond the space bands’ range.
With the matrices aligned and the space bands set to the correct measure, the machine then ‘locks up’ the line with great force and the plunger injects the molten type metal into the space created by the mold cavity and the assembled line. The machine then separates the mold disk (carrying the freshly cast slug), the metal pot, and the first elevator. The mold disk then turns to present the line at the ejecting position, in the process passing by a knife that trims the base of the slug to type height (0.918″ on US machines). The slug is then forced through an adjustable pair of knives to trim the slug to the proper body height before sliding down into a ‘galley’ of finished lines next to the operator. Depending on the model of machine, the mold disk could have four (standard), six, or two molds, giving the operator his choice of line lengths and body sizes.
As the mold disk is turning, the first elevator simultaneously rises to its upper position and the space bands and matrices are vertically aligned in preparation for the second transfer. The matrices have a series of teeth in a V-shaped notch on top, and as the transfer is completed, the matrices slide onto the second elevator bar which carries the matrices by these V-shaped notches. The space bands, having no such notches, remain in the second transfer channel and are soon gathered by two levers and pushed back into the space band box. While the space bands are being pushed into their box, the second elevator continues rising towards the distributing mechanism at the top of the machine, which returns the molds to their proper places in the magazine. At the top of the machine, a lever (the distributor shifter) moves left to get in position to push the incoming line of matrices off the second elevator and into the distributor box. This mechanism feeds the matrices at precise intervals such that they travel between three rotating screws. Each matrix is carried along a notched bar between the three screws until the notches on the bar and matrix match, whereupon the matrix drops down into its proper channel in the magazine.
It was a source of pride for trained operators to boast of being able to ‘hang’ a line – to keep a line waiting in the delivery channel while the machine was casting the previous line and the operator was composing the next one.
The metal pot was kept filled by the operator tossing in small ingots of type metal every few lines, or later, by mechanical feeders that carry large ingots of type metal (and which often carried two ‘pigs’ at a time to be consumed in turn, the operator hanging a fresh one when one was consumed). These feeders are actuated by various methods (by cam, either elevator, or distributor shifter), but the result is the same – the ingots are fed little by little into the pot, keeping it filled to the correct level.