Tin

Tin is Jupiter in the alchemical scheme. Its symbol resembles the numeral four, and in Latin texts the metal is frequently called simply Jupiter or Jove.

Of the seven correspondences this is the one for which the reasoning is least evident, and the honest thing is to say so. Gold and the Sun, silver and the Moon, mercury and Mercury, iron and Mars, lead and Saturn all have an obvious hook in colour, speed, name or weight. Tin and Jupiter has none that the sources make explicit. The usual reconstructions appeal to position in the ordering: the seven metals were mapped onto the seven planets in their classical sequence of distance or of apparent speed, and tin falls where Jupiter falls. Some accounts associate the whiteness and brightness of tin with Jupiter's brilliance as the second-brightest planet. Neither explanation is documented as the original rationale.

What is documented is the association itself, which is stable across the corpus from late antiquity onward and appears alongside the other six in medieval and early modern texts alike. The word jovial, meaning cheerful, comes from the astrological character of Jupiter rather than from anything about the metal, and the two should not be run together.

Tin's practical role in the tradition was as a component of alloys and as a source of its oxide. Tin oxide is a white opacifier, and tin-glazed earthenware, the white surface on which maiolica, delftware and Islamic lustreware are painted, depends on it. That technology reached Europe through the Islamic world from around the ninth century.

Copper alone is soft. Copper with about ten per cent tin is bronze, which is markedly harder, pours into a mould more cleanly, and takes and keeps an edge. The difference is large enough that the alloy names an age.

The problem with bronze is geological. Copper ore is widespread. Tin ore, essentially cassiterite, is not; it occurs in a small number of places and almost never near copper. Making bronze therefore required something no earlier technology had needed: sustained long-distance exchange between regions that had never had reason to deal with one another.

The tin came from Cornwall and Devon, from Iberia, from Brittany, from central Asia and from what is now Afghanistan. Analysis of trace elements and isotopes in Bronze Age objects has traced tin moving across thousands of kilometres. The Cassiterides, the tin islands of Greek and Roman geography, were a real trade destination whose location was a commercial secret; Herodotus admits he does not know where they are. The Uluburun shipwreck off the Turkish coast, dated to the late fourteenth century BCE, was carrying about ten tonnes of copper and roughly one tonne of tin, close to the correct ratio for bronze, which is as direct a piece of evidence for the trade as could be asked for.

The dependence cut both ways. A civilisation whose weapons and tools required an imported material from a small number of distant sources was fragile in a specific way, and the disruption of those routes is one of the standard elements in explanations of the Late Bronze Age collapse around 1200 BCE. Iron, whose ore is everywhere, carried no such vulnerability.

Tin does two odd things that were noticed long before they were understood.

The first is the tin cry. Bending a bar of tin produces an audible crackling, caused by crystal planes slipping past one another. It is a simple test for the metal and has been used as one.

The second is tin pest. Below about 13 degrees C the ordinary metallic form, white tin, is no longer the stable one; it converts slowly to grey tin, a brittle powdery semiconductor with a different crystal structure and a substantially larger volume. The conversion is slow near the transition temperature and faster in severe cold, and it spreads outward from a nucleation point, which is why it looks like a disease. Tin organ pipes, pewter vessels and tin buttons left in unheated buildings through hard winters have crumbled to grey dust, and the effect was attributed to the devil before it was attributed to crystallography. The story that Napoleon's army in Russia lost its uniform buttons this way is frequently repeated and is not supported by evidence; the phenomenon is real, that particular case is not established.

Tin's modern life is chiefly as a coating and as solder. The tin can, patented by Peter Durand in 1810, is steel with a thin tin lining, tin being non-toxic and resistant to food acids, and it changed the storage and transport of food permanently. Tin-lead solder joined electronic assemblies for most of the twentieth century until lead was legislated out, and tin-based alloys replaced it. Pewter is tin with copper and antimony; bell metal and speculum metal are high-tin bronzes.