In printing, type metal refers to the metal alloys used in traditional typefounding and hot metal typesetting. Historically, type metal was an alloy of lead, tin and antimony in different proportions depending on the application, be it individual character mechanical casting for hand setting, mechanical line casting or individual character mechanical typesetting and stereo plate casting. The proportions used are in the range: lead 50‒86%, antimony 11‒30% and tin 3‒20%. 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. It should also be easy to cast, at reasonable low melting temperature, iron should not dissolve in the molten metal, and mould and nozzles should stay clean and easy to maintain. Today, Monotype machines can utilize a wide range of different alloys. Mechanical linecasting equipment uses alloys that are close to eutectic.
History
Although the knowledge of casting soft metals in moulds was well established before Johannes Gutenberg's time, his discovery of an alloy that was hard, durable, and would take a clear impression from the mould represents a fundamental aspect of his solution to the problem of printing with movable type. This alloy did not shrink as much as lead alone when cooled. 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.
Required characteristics Cheap, plentifully available as galena and easily workable, lead has many of the ideal characteristics, but on its own it lacks the necessary hardness and does not make castings with sharp details because molten lead shrinks and sags when it cools to a solid. 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. Despite patiently trying different proportions of both metals, solving the second part of the type metal problem proved very difficult without the addition of yet a third metal, antimony. Alchemists had shown that when stibnite, an antimony sulfide ore, was heated with scrap iron, metallic antimony was produced. The typefounder would typically introduce powdered stibnite and horseshoe nails into his crucible to melt lead, tin and antimony into type metal. Both the iron and the sulfides would be rejected in the process. The addition of antimony conferred the much needed improvements in the properties of hardness, wear resistance and especially, the sharpness of reproduction of the type design, given that it has the curious property of diminishing the shrinkage of the alloy upon solidification.
Composition of type metal Type metal is an alloy of lead, tin and antimony in different proportions depending on the application, be it individual character mechanical casting for hand setting, mechanical line casting or individual character mechanical typesetting and stereo plate casting. The proportions used are in the range: lead 50‒86%, antimony 11‒30% and tin 3‒20%. The basic characteristics of these metals are as follows:
Lead Type metal is an alloy of lead (Pb). Pure lead is a relatively cheap metal, is soft thus easy to work, and it is easy to cast since it melts at 327 °C (621 °F). However, it shrinks when it solidifies making letters that are not sharp enough for printing. In addition pure lead letters will quickly deform during use; a direct result of the easy workability of lead. Lead is exceptionally soft, malleable, and ductile but with little tensile strength. Lead oxide is a poison, that primarily damages brain function. Metallic lead is more stable and less toxic than its oxidized form. Metallic lead cannot be absorbed through contact with skin, so may be handled, carefully, with far less risk than lead oxide.
Tin Tin (Sn) promotes the fluidity of the molten alloy and makes the type tough, giving the alloy resistance to wear. It is harder, stiffer and tougher than lead.
Antimony Antimony (Sb) is a metalloid element, which melts at 630 °C (1,166 °F). Antimony has a crystalline appearance while being both brittle and fusible. When alloyed with lead to produce type metal, antimony gives it the hardness it needs to resist deformation during printing, and gives it sharper castings from the mould to produce clear, easily read printed text on the page.
Typical type metal proportions The actual compositions differed over time, different machines were adjusted to different alloys depending on the intended uses of the type. Printers had sometimes their own preferences about the quality of particular alloys. The Lanston Monotype Corporation in the United Kingdom had a whole range of alloys listed in their manuals.
Alloys for mechanical composition Most mechanical typesetting is divided basically into two different competing technologies: line casting (Linotype and Intertype) and single character casting (Monotype). 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. Although in general Monotype cast type characters can be visually identified as having a square nick (as opposed to the round nicks used on foundry type), there is no easy way to identify the alloy aside from an expensive chemical assay in a laboratory. Apart from this the two Monotype companies in the United States and the UK also made moulds with 'round' nicks. Typefounders and printers could and did order specially designed moulds to their own specifications: height, size, kind of nick, even the number of nicks could be changed. Type produced with these special moulds can only be identified if the foundry or printer is known.
In Switzerland the company "Metallum Pratteln AG", in Basel had yet another list of type-metal alloys. If needed, any alloy according to customer specifications could be produced.
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