Letter metal
Letter metal is the name of a lead alloy that is used for the casting of movable letters , the printing types.
In the graphic arts industry, lead types were common until the 1970s. The printing processes are today largely based on z. B. Offset process changed.
The letter metal in the strict sense was composed of lead and 5 to 6% tin and 28 to 29% antimony , sometimes also a little copper . Until the 19th century, the alloys were mostly contaminated, so that not only zinc , aluminum , nickel and iron , but also the poisonous arsenic could be found in the metal. Arsenic is a common by-product in the manufacture of lead alloys, but it also increases the hardness of the metal. In the course of technical progress, the impurities could be limited to 0.01 to 0.05%.
The main component lead gives the “stuff” (old name for letter metal) the softness and malleability, antimony the necessary hardness, the tin ensures a good connection of the individual metals and a corresponding toughness and abrasion resistance. Copper increases the hardness and resistance of the font.
In addition, other alloys were used for each special case of type casting:
- Back-casting metal (lead, tin 2.5–3.5%, antimony 3.5 to 4.5%)
- Typo (graph) metal (lead, tin 2.5–3.5%, antimony 11.5 to 12.5%) for blank material on Typograph typesetting machines
- Lino (type) metal (lead, tin 4.5–5.5%, antimony 11.5 to 12.5%) for Linotype typesetting machines
- Mono (type) metal (lead, tin 8.5–9.5%, antimony 18.5 to 19.5%) for monotype casting machines
- Note metal (lead, tin 15.5–16%, antimony 4 to 5%) for note engraving plates.
- Reglettenmetall
- Exclusion metal
- Stereotype metal
- and many more
The variety of alloys is explained by the special requirements: Individual types for manual set were used again and again and therefore had to be robust. Casting machines optimized for the lead machine set could only be operated trouble-free with alloys that were precisely matched to these.
Zinc interferes with z. B. the flow behavior and the formation of an oxide skin, copper crystals can clog the pouring mouth if the concentration is too high. Due to burn-off and dross formation, the concentration ratios in the melt change during operation, so this is compensated for with additional metal (also of a defined composition).
Individual evidence
- ↑ DAS PFEIFENWERK (organ information) , private website
- ^ Römpp Chemielexikon, Volume 1, page 253, 9th edition 1989