Type metal
Encyclopedia
In printing, type metal (sometimes called hot metal) refers to the metal alloy
s used in traditional typefounding
and hot metal typesetting
. Lead is the main constituent of these alloys. Antimony and tin are added to make the character produced durable and tough while reducing the difference between the coefficients of expansion of the matrix and the alloy.
s 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
. (His other contributions were 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.)
The enormous effort to create an alloy with the characteristics needed in an ideal type metal is often underestimated.
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 pewter
er'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.
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:
The basis for type metal is lead, a relatively cheap metal, that melts at 621 °F. It is easy to handle and makes alloys with many other metals. It is, however, very soft and castings with pure lead are not sharp enough for printing. Lead is poisonous and very heavy.
Lead is exceptionally soft, malleable and ductile but with little tenacity. Easily fusible with other metals, it does not produce sharply defined castings.
This soft metal has a low melting point at 450 °F. Tin 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 melts at 1166 °F. This highly crystalline metalloid, gives type metal its hardness and a much better and sharper cast from the matrix. It has a crystalline appearance while being both brittle and fusible. When alloyed with lead, it strengthens the alloy and improves casting detail.
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 US 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.
Type metal alloys mentioned in the UK-Monotype-caster manuals
Sn/Sb
liquid at solid at
Hardness purpose>
1 6/15
502 °F 464 °F
23.0 Brinell routine>
2 10/16
524 °F 464 °F
27.0 Brinell dual = machine & hand composition>
3 9/19
546 °F 464 °F
28.5 Brinell routine machine composition>
4 13/17
542 °F 464 °F
29.5 Brinell catalogues>
5 12/24
626 °F 464 °F
33 Brinell display type, heavy duty jobs>
In Switzerland the compagny "Metallum Pratteln AG", in Basel had yet another list of type-metal alloys. If needed, any alloy according to customer specifications could be produced.
to replace lost tin and antimony through the "dross".
Every time type metal is remelted, tin and antimony oxidise. These oxides form on the surface of the crucible and must be removed. After stirring some grey powder the dross will be left. This dross still contains type metal.
Dross must be processed at specialized companies, in order to extract the pure metals in conditions that would prevent environmental pollution
.
Example: addition of a small amount of antimony some 5 or 6% :
Although the melting point of antimony is 1166 °F, this mixture will be completely molten and a homogeneous fluid at 700 °F.
Cooling down, at 671 °F, the melting point of pure lead, nothing will happen.
After cooling down until 555 °F, lead crystal
s will start to grow. This will make the fluid more and more pasty. The temperature will drop until 486 °F, before solidification starts. Only when the fluid has become completely solid, and all melting-energy is lost to the environment, will the temperature lower again.
A mixture of 10% antimony and 90% lead: the formation of the crystals will only start later at a lower temperature of some 500 °F. After this the temperature will drop to 486 °F, and remain there until solidification is complete again.
An alloy with 12% antimony and 88% lead has a sharp melting point at 486 °F. No crystallisation will occur above this temperature.
This mixture is called: eutectic
.
Higher contents of antimony will raise the temperature where crystallisation starts. This crystals contain a high content of antimony depleting the fluid of this metal, until the fluid becomes eutectic at last.
The resulting solid contains smaller and larger crystals of antimony surrounded by a small crystalline -almost fibric- eutectic.
Depending from the metals in excess, compared with the eutectic, crystals are formed, depleting the liquid, until the eutectic 4/12 mixture is formed once more.
The 12/20 alloy contains many mixed crystals of tin and antimony, these crystals constitute the hardness of the alloy and the resistance against wear.
Raising the content of antimony cannot be done without adding some tin too. Because the fluidity of the mixture will dramatically diminish when the temperature goes down somewhere in the channels of the machine. Nozzles can be blocked by antimony crystals.
Alloys used on Monotype machines tend to contain higher contents of tin, to obtain tougher character. All characters should be able to resist the pressure during printing. This meant an extra investment, but Monotype was an expensive system all the way.
and Monotype
has given rise to some lasting fairy tales around typemetal. Linotype users looked down on Monotype and vice versa.
Monotype machines however can utilize a wide of different alloys; maintaining a constant and a high production meant a strict standardization of the typemetal in the company, so as to reduce by all means any interruption of the production. 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. These oxides are removed with the dross
while cleaning the surface of the molten metal.
Nowadays this "battle" has lost its importance for a good deal, at least for Monotype. The quality of the produced type is far more important. 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.
Although care was taken to avoid mixing different types of type metal in shops with different type casting systems, in actual practice this often occurred. Since a Monotype composition caster can cope with a variety of different metal alloys, occasional mixing of Linotype alloy with discarded typefounders alloy has proven its usefulness.
Mechanical linecasting equipment use alloys that are close to eutectic.
has been used for hardening type metal; this metal easily forms mixed crystals with tin when the alloy cools down. These crystals will grow just below the exit opening of the nozzle in Monotype machines, resulting in a total blockage after some time. These nozzles are very difficult to clean, because the hard crystals will resist drilling.
spaces contain zinc
, which is extremely counterproductive in type metal. Even a tiny amount — less than 1% — will form a dusty surface on the molten metal surface that is difficult to remove. Characters cast from contaminated type metal such as this are of inferior quality, the solution being to discard and replace with fresh alloy.
Brass and zinc should therefore be removed before remelting. 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.
plates are very dangerous in molten lead, because this metal can easily burn and will ignite in this way the metal in the pot.
is hardly dissolved into type metal, although the molten metal is always in contact with the cast iron surface of the melting pot.
s', in his Mechanick Exercises, mentions a mix of equal amounts of "antimony" and iron nails.
The "antimony" here was in fact stibnite
, antimony-sulfide (Sb2S3). The iron was burned away in this process, reducing the antimony and while removing the unwanted sulfur
. In this way ferro-sulfide is formed, and this will evaporate with the fumes.
The mixture of stibnite and nails was heated red hot in an open-air furnace
, until all is molten and finished. The resulting metal can contain up to 9% of iron. Further purification can be done by mixing the hot melt with kitchen-salt, NaCl. After this red hot lead from another melting pot is added and stirred thoroughly.
Some tin was added to the alloy for casting small characters and narrow spaces, to better fill narrow areas of the mould. The good properties of tin were well known. The use of tin was sometime minimized to save expenses.
Much of this toxic work was done by child labour, a labor force
that includes child
ren.
As a supposed antidote
to the inhaled toxic metal fumes, the workers were given a mixture of red wine and salad oil:
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s used in traditional typefounding
Movable type
Movable type is the system of printing and typography that uses movable components to reproduce the elements of a document ....
and hot metal typesetting
Hot metal typesetting
In printing and typography, hot metal typesetting refers to 19th-century technologies for typesetting text in letterpress printing. This method injects molten type metal into a mold that has the shape of one or more glyphs...
. Lead is the main constituent of these alloys. Antimony and tin are added to make the character produced durable and tough while reducing the difference between the coefficients of expansion of the matrix and the alloy.
History
Although the knowledge of casting soft metals in mouldMolding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....
s 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
Printing
Printing is a process for reproducing text and image, typically with ink on paper using a printing press. It is often carried out as a large-scale industrial process, and is an essential part of publishing and transaction printing....
with movable type
Movable type
Movable type is the system of printing and typography that uses movable components to reproduce the elements of a document ....
. (His other contributions were 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.)
The enormous effort to create an alloy with the characteristics needed in an ideal type metal is often underestimated.
Required characteristics
Cheap, plentifully available as galenaGalena
Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...
and easily workable, lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
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 pewter
Pewter
Pewter is a malleable metal alloy, traditionally 85–99% tin, with the remainder consisting of copper, antimony, bismuth and lead. Copper and antimony act as hardeners while lead is common in the lower grades of pewter, which have a bluish tint. It has a low melting point, around 170–230 °C ,...
er's tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
, obtained from cassiterite
Cassiterite
Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem...
, 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
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
.
Alchemists
Alchemy
Alchemy is an influential philosophical tradition whose early practitioners’ claims to profound powers were known from antiquity. The defining objectives of alchemy are varied; these include the creation of the fabled philosopher's stone possessing powers including the capability of turning base...
had shown that when stibnite
Stibnite
Stibnite, sometimes called antimonite, is a sulfide mineral with the formula Sb2S3. This soft grey material crystallizes in an orthorhombic space group. It is the most important source for the metalloid antimony...
, an antimony sulfide ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....
, 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
Type design
Type design is the art of designing typefaces.- History :Although the technology of printing text using movable type was invented in China, and despite the esteem which calligraphy held in that civilization, the vast number of Chinese characters meant that few distinctive, complete fonts could be...
, 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 of metal 10b, or 613The basis for type metal is lead, a relatively cheap metal, that melts at 621 °F. It is easy to handle and makes alloys with many other metals. It is, however, very soft and castings with pure lead are not sharp enough for printing. Lead is poisonous and very heavy.
Lead is exceptionally soft, malleable and ductile but with little tenacity. Easily fusible with other metals, it does not produce sharply defined castings.
Tin
type of metal 24snoThis soft metal has a low melting point at 450 °F. Tin 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
type of metal 623Antimony melts at 1166 °F. This highly crystalline metalloid, gives type metal its hardness and a much better and sharper cast from the matrix. It has a crystalline appearance while being both brittle and fusible. When alloyed with lead, it strengthens the alloy and improves casting detail.
Typical type metal proportions
The actual compositions differed over time and with different machines and intended uses. Monotype Corporation had a whole range of alloys listed in their manuals.| Alloy type | Tin | Antimony | Lead | Comments |
|---|---|---|---|---|
| Slugcasting alloy | 3% | 11% | 86% | Ludlow/Intertype/Linotype composition for limited use and for making stereos |
| Eutectic alloy | 4% | 12% | 84% | Often used on slug casters and for Monotype/Elrod spacing material |
| Stereotype alloy | 7% | 15% | 78% | More durable intended for long print runs and curved printing plates |
| Monotype alloy | 10% | 16% | 74% | Most durable machine set intended to be remelted, sometimes hand set |
| Foundry type alloy | 18% | 28% | 54% | Traditional loose hand set type, may contain some copper |
Alloys for mechanical composition
Most mechanical typesetting is divided basically into two different competing technologies: line casting (LinotypeLinotype machine
The Linotype typesetting machine is a "line casting" machine used in printing. The name of the machine comes from the fact that it produces an entire line of metal type at once, hence a line-o'-type, a significant improvement over manual typesetting....
and Intertype
Intertype Corporation
The Intertype Corporation produced the Intertype, a typecasting machine closely resembling the Linotype, and using the same matrices as the Linotype...
) and single character casting (Monotype
Monotype Corporation
Monotype Imaging Holdings is a Delaware corporation based in Woburn, Massachusetts and specializing in typesetting and typeface design as well as text and imaging solutions for use with consumer electronics devices. Monotype Imaging Holdings is the owner of Monotype Imaging Inc., Linotype,...
).
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
Nick
Nick may refer to:*A short form for Nicholas or Nikhil*Nick , an element of DNA structure*Nickelodeon , a television network**Nickelodeon , for other versions of Nickelodeon and their sister channels around the globe....
(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
Assay
An assay is a procedure in molecular biology for testing or measuring the activity of a drug or biochemical in an organism or organic sample. A quantitative assay may also measure the amount of a substance in a sample. Bioassays and immunoassays are among the many varieties of specialized...
in a laboratory.
Apart from this the two Monotype companies in the US 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.
Type metal alloys mentioned in the UK-Monotype-caster manuals
In Switzerland the compagny "Metallum Pratteln AG", in Basel had yet another list of type-metal alloys. If needed, any alloy according to customer specifications could be produced.
| Usage | Sn/Sb | liquid at | casting at | remelting at | Hardness |
|---|---|---|---|---|---|
| Typograph | 3/12 | 250 °C | 280-290 °C | 310-330 °C | 19 |
| Ludlow | 5/12 | 245 °C | 270-285 °C | 300-320 °C | 21 |
| Lino/Intertype a | 5/12 | 245 °C | 270-285 °C | 300-320 °C | 21 |
| Lino/Intertype b | 6/12 | 243 °C | 270-285 °C | 300-320 °C | 21.5 |
| Lino/Intertype c | 7/12 | 241 °C | 270-285 °C | 300-320 °C | 22 |
| Stereotyping | 5/15 | 265 °C | 320 °C | 320-340 °C | 23 |
| Stereotyping | 7/14 | 258 °C | 315 °C | 320-340 °C | 23 |
| Monotype a | 5/15 | 265 °C | 350 °C | 330-350 °C | 23 |
| Monotype b | 8/15 | 260 °C | 360 °C | 350-370 °C | 25 |
| Monotype c | 7/17 | 280 °C | 370 °C | 360-380 °C | 26 |
| Monotype d | 9/19 | 285 °C | 390 °C | 380-400 °C | 28.5 |
| Monotype e | 9.5/15 | 270 °C | 360 °C | 350-370 °C | 26 |
| Monotype f | 9.5/17 | 280 °C | 380 °C | 370-390 °C | 27.5 |
| Monotype g | 10/16 | 275 °C | 370 °C | 360-380 °C | 27 |
| Regeneration a | 9/11 | . | . | . | . |
| Regeneration b | 9/12 | . | . | . | . |
| Regeneration c | 9/16 | . | . | . | . |
| Support metal a | 1/2 | 310 °C | . | 360-380 °C | 6 |
| Support metal b | 3/5 | 295 °C | . | 340-360 °C | 14 |
| Support metal c | 5/5 | 280 °C | . | 340-360 °C | 16 |
| Typefounding | 5.5/28.5 | 360 °C | . | 420-430 °C | 29.5 |
Dross
Regeneration-metal was melted into the crucibleCrucible
A crucible is a container used for metal, glass, and pigment production as well as a number of modern laboratory processes, which can withstand temperatures high enough to melt or otherwise alter its contents...
to replace lost tin and antimony through the "dross".
Every time type metal is remelted, tin and antimony oxidise. These oxides form on the surface of the crucible and must be removed. After stirring some grey powder the dross will be left. This dross still contains type metal.
Dross must be processed at specialized companies, in order to extract the pure metals in conditions that would prevent environmental pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
.
General requirements for type-metal
- Type metal should produce a true and sharp cast, and reproduce the matrix in all detail. The dimensions and form should be correct after cooling down.
- Type metal should be strong and lasting, to endure wear and pressure while printing.
- Type metal should be easy to cast, this means: a reasonable low melting temperatureMelting temperatureMelting temperature may refer to:* Melting point, the temperature at which a substance changes from solid to liquid state.* DNA melting temperature, the temperature at which a DNA double helix dissociates into single strands....
, iron should not dissolve in the molten metal, mould and nozzles should stay clean and easy to maintain. - The molten metal should be clean, while molten it should give as little dross as possible, to prevent loss of tin and antimony.
- The economics have to be taken in account too: keeping the costs down would mean: keeping the content of tin and antimony as low as possible, and maintaining a high quality of the type produced.
- Type metal should not adhere to the copper of the matrix.
Behaviour of bipolar alloys
Pure metal melts and solidifies in a simple manner at a specific temperature. This is not the case with alloys. There we find a range of temperatures with all kinds of different events. The melting temperature of all mixtures is considerably lower than the pure components.Example: addition of a small amount of antimony some 5 or 6% :
Although the melting point of antimony is 1166 °F, this mixture will be completely molten and a homogeneous fluid at 700 °F.
Cooling down, at 671 °F, the melting point of pure lead, nothing will happen.
After cooling down until 555 °F, lead crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
s will start to grow. This will make the fluid more and more pasty. The temperature will drop until 486 °F, before solidification starts. Only when the fluid has become completely solid, and all melting-energy is lost to the environment, will the temperature lower again.
A mixture of 10% antimony and 90% lead: the formation of the crystals will only start later at a lower temperature of some 500 °F. After this the temperature will drop to 486 °F, and remain there until solidification is complete again.
An alloy with 12% antimony and 88% lead has a sharp melting point at 486 °F. No crystallisation will occur above this temperature.
This mixture is called: eutectic
Eutectic system
A eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition. This composition is known as the eutectic composition and the temperature is known as the eutectic temperature...
.
Higher contents of antimony will raise the temperature where crystallisation starts. This crystals contain a high content of antimony depleting the fluid of this metal, until the fluid becomes eutectic at last.
The resulting solid contains smaller and larger crystals of antimony surrounded by a small crystalline -almost fibric- eutectic.
Tri-polar mixtures
Adding tin to this bipolar-system complicates the behaviour even further. Some tin enters into the eutectic. Which has the composition of 4% per cent Tin, 12 per cent Antimony and 84 per cent lead, this mixture solifies at 464 °F.Depending from the metals in excess, compared with the eutectic, crystals are formed, depleting the liquid, until the eutectic 4/12 mixture is formed once more.
The 12/20 alloy contains many mixed crystals of tin and antimony, these crystals constitute the hardness of the alloy and the resistance against wear.
Raising the content of antimony cannot be done without adding some tin too. Because the fluidity of the mixture will dramatically diminish when the temperature goes down somewhere in the channels of the machine. Nozzles can be blocked by antimony crystals.
Metals used on typecasting machines
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. All characters should be able to resist the pressure during printing. This meant an extra investment, but Monotype was an expensive system all the way.
Present usage of type metal
The fierce competition between the different mechanical typecasting systems like LinotypeLinotype machine
The Linotype typesetting machine is a "line casting" machine used in printing. The name of the machine comes from the fact that it produces an entire line of metal type at once, hence a line-o'-type, a significant improvement over manual typesetting....
and Monotype
Monotype Corporation
Monotype Imaging Holdings is a Delaware corporation based in Woburn, Massachusetts and specializing in typesetting and typeface design as well as text and imaging solutions for use with consumer electronics devices. Monotype Imaging Holdings is the owner of Monotype Imaging Inc., Linotype,...
has given rise to some lasting fairy tales around typemetal. Linotype users looked down on Monotype and vice versa.
Monotype machines however can utilize a wide of different alloys; maintaining a constant and a high production meant a strict standardization of the typemetal in the company, so as to reduce by all means any interruption of the production. 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. These oxides are removed with the dross
Dross
Dross is a mass of solid impurities floating on a molten metal. It appears usually on the melting of low-melting-point metals or alloys such as tin, lead, zinc or aluminium, or by oxidation of the metal. It can also consist of impurities such as paint leftovers...
while cleaning the surface of the molten metal.
Nowadays this "battle" has lost its importance for a good deal, at least for Monotype. The quality of the produced type is far more important. 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.
Although care was taken to avoid mixing different types of type metal in shops with different type casting systems, in actual practice this often occurred. Since a Monotype composition caster can cope with a variety of different metal alloys, occasional mixing of Linotype alloy with discarded typefounders alloy has proven its usefulness.
Mechanical linecasting equipment use alloys that are close to eutectic.
Copper
CopperCopper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
has been used for hardening type metal; this metal easily forms mixed crystals with tin when the alloy cools down. These crystals will grow just below the exit opening of the nozzle in Monotype machines, resulting in a total blockage after some time. These nozzles are very difficult to clean, because the hard crystals will resist drilling.
Zinc
BrassBrass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
spaces contain zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, which is extremely counterproductive in type metal. Even a tiny amount — less than 1% — will form a dusty surface on the molten metal surface that is difficult to remove. Characters cast from contaminated type metal such as this are of inferior quality, the solution being to discard and replace with fresh alloy.
Brass and zinc should therefore be removed before remelting. The same applies to aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, although this metal will float on top of the melt, and will be easily discovered and removed, before it is dissolved into the lead.
Magnesium
MagnesiumMagnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
plates are very dangerous in molten lead, because this metal can easily burn and will ignite in this way the metal in the pot.
Iron
IronIron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
is hardly dissolved into type metal, although the molten metal is always in contact with the cast iron surface of the melting pot.
Historic references to type metals
Joseph MoxonJoseph Moxon
Joseph Moxon , hydrographer to Charles II, was an English printer of mathematical books and maps, a maker of globes and mathematical instruments, and mathematical lexicographer. He produced the first English language dictionary devoted to mathematics...
s', in his Mechanick Exercises, mentions a mix of equal amounts of "antimony" and iron nails.
The "antimony" here was in fact stibnite
Stibnite
Stibnite, sometimes called antimonite, is a sulfide mineral with the formula Sb2S3. This soft grey material crystallizes in an orthorhombic space group. It is the most important source for the metalloid antimony...
, antimony-sulfide (Sb2S3). The iron was burned away in this process, reducing the antimony and while removing the unwanted sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
. In this way ferro-sulfide is formed, and this will evaporate with the fumes.
The mixture of stibnite and nails was heated red hot in an open-air furnace
Furnace
A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...
, until all is molten and finished. The resulting metal can contain up to 9% of iron. Further purification can be done by mixing the hot melt with kitchen-salt, NaCl. After this red hot lead from another melting pot is added and stirred thoroughly.
Some tin was added to the alloy for casting small characters and narrow spaces, to better fill narrow areas of the mould. The good properties of tin were well known. The use of tin was sometime minimized to save expenses.
Much of this toxic work was done by child labour, a labor force
Labor force
In economics, a labor force or labour force is a region's combined civilian workforce, including both the employed and unemployed.Normally, the labor force of a country consists of everyone of working age In economics, a labor force or labour force is a region's combined civilian workforce,...
that includes child
Child
Biologically, a child is generally a human between the stages of birth and puberty. Some vernacular definitions of a child include the fetus, as being an unborn child. The legal definition of "child" generally refers to a minor, otherwise known as a person younger than the age of majority...
ren.
As a supposed antidote
Antidote
An antidote is a substance which can counteract a form of poisoning. The term ultimately derives from the Greek αντιδιδοναι antididonai, "given against"....
to the inhaled toxic metal fumes, the workers were given a mixture of red wine and salad oil: