Type metal

Antimony and tin are added to lead for durability while reducing the difference between the coefficients of expansion of the matrix and the alloy.

Apart from durability, the general requirements for type-metal are that it should produce a true and sharp cast, and retain correct dimensions and form after cooling down.

Gutenberg's other contributions were the creation of inks that would adhere to metal type and a method of softening handmade printing paper so that it would take the impression well.

After much experimentation it was found that adding pewterer's tin, obtained from cassiterite, improved the ability of the cast type to withstand the wear and tear of the printing process, making it tougher but not more brittle.

The typefounder would typically introduce powdered stibnite and horseshoe nails into his crucible to melt lead, tin and antimony into type metal.

The manuals for the Monotype composition caster (1952 and later editions) mention at least five different alloys to be used for casting, depending the purpose of the type and the work to be done with it.

After stirring the molten metal, grey powder forms on the surface, the dross, needing to be skimmed.

Dross must be processed at specialized companies, in order to extract the pure metals in conditions that would prevent environmental pollution and remain economically feasible.

Once the temperature reaches 291 °C, lead crystals will start to form, increasing the cohesion of the liquid alloy.

Eutectic alloys are used on Linotype-machines and Ludlow-casters to prevent blockage of the mould and to ensure continuous trouble-free casting.

Alloys used on Monotype machines tend to contain higher contents of tin, to obtain tougher character.

The fierce competition between the different mechanical typecasting systems like Linotype and Monotype has given rise to some lasting fairy tales about typemetal.

Repeated assays were done at regular intervals to monitor the alloy used, since every time the metal is recycled, roughly half a per cent of tin content is lost through oxidation.

Alloys with a high-content of antimony, and subsequently a high content of tin, can be cast at a higher temperature, and at a lower speed and with more cooling at a Monotype composition or supercaster.

These crystals will grow just below the exit opening of the nozzle in Monotype machines, resulting in a total blockage after some time.

Characters cast from contaminated type metal such as this are of inferior quality, the solution being to discard and replace with fresh alloy.

The same applies to aluminium, although this metal will float on top of the melt, and will be easily discovered and removed, before it is dissolved into the lead.

Joseph Moxon, in his Mechanick Exercises, mentions a mix of equal amounts of "antimony" and iron nails.

To make the Iron Run, they mingle an equal weight of Antimony (beaten in an Iron-Morter into small pieces) and stub-Nails together.

And preparing so many Earthen forty or fifty pounds Melting-pots (made for that purpose to endure the Fire) as they intend to use: They Charge these Pots with the mingeld Iron and Antimony as full as they will hold.

They make it of bricks in an open place, as well because the air may have free access to all its sides, as that the vapours of the Antimony (which are obnoxious) may the less offend those that officiate at the Making the Mettal: And also because the violent fire made in the Furnace should not endanger the Firing any adjacent Houses.The "antimony" here was in fact stibnite, antimony-sulfide (Sb2S3).

The mixture of stibnite and nails was heated red hot in an open-air furnace, until all is molten and finished.

[5] Hitherto a Man (nay, a Boy) might officiate all this work.As a supposed antidote to the inhaled toxic metal fumes, the workers were given a mixture of red wine and salad oil:[6] Now (according to Custom) is Half a Pint of Sack mingled with Sallad Oyl, provided for each Workman to drink; intended or an Antidote against the Poysonous Fumes of the Antimony, and to restore the Spirits that so Violent a Fire and Hard Labour may have exhausted.