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. Antimony has a crystalline appearance while being both brittle and fusible. It is harder, stiffer and tougher than lead.Īntimony (Sb) is a metalloid element, which melts at 630 ☌ (1,166 ☏). Tin (Sn) promotes the fluidity of the molten alloy and makes the type tough, giving the alloy resistance to wear.
Metallic lead cannot be absorbed through contact with skin, so may be handled, carefully, with far less risk than lead oxide.
Metallic lead is more stable and less toxic than its oxidized form. Lead oxide is a poison, that primarily damages brain function. Lead is exceptionally soft, malleable, and ductile but with little tensile strength. In addition pure lead letters will quickly deform during use a direct result of the easy workability of lead. However, it shrinks when it solidifies making letters that are not sharp enough for printing. Pure lead is a relatively cheap metal, is soft thus easy to work, and it is easy to cast since it melts at 327 ☌ (621 ☏). The basic characteristics of these metals are as follows: The proportions used are in the range: lead 50‒86%, antimony 11‒30% and tin 3‒20%. 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 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. Both the iron and the sulfides would be rejected in the process. The typefounder would typically introduce powdered stibnite and horseshoe nails into his crucible to melt lead, tin and antimony into type metal. (His 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.)Ĭheap, 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.Īfter 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.ĭespite 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.Īlchemists had shown that when stibnite, an antimony sulfide ore, was heated with scrap iron, metallic antimony was produced. Mechanical linecasting equipment uses alloys that are close to eutectic.ġ698 illustration of a German typefounder preparing type-metalĪlthough 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 (because it did not shrink as much as lead alone when cooled) represents a fundamental aspect of his solution to the problem of printing with movable type. Today, Monotype machines can utilize a wide range of different alloys. 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. 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. Antimony and tin are added to lead for durability while reducing the difference between the coefficients of expansion of the matrix and the alloy. 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. In printing, type metal refers to the metal alloys used in traditional typefounding and hot metal typesetting.