On the cover of the third volume of his great German Social History the historian Hans-Ulrich Wehler has used a painting from the year 1889, depicting the visit of the Grand Duke of Saxony to the iron foundry of Asolda. Nothing seemed to the author to represent the formative years of German industry more clearly than that painting. Wehler illustrates the pace of industrialisation with a statistic – between the years 1850 to 1873 the annual production of steel in Germany grew eightfold from about 200,000 to 1,600,000 tonnes. Without steel, no industrialisation.

It is not simply coincidence that his contemporary Richard Wagner, in ‘The Ring of the Nibelung’, elevated iron and steel processing to mythical proportions when his Siegfried, ‘the man who never knew fear’, first succeeds in forging the magical sword ‘Notung’. Industrialisation finds in this towering work memories of the ancient German myths. A hero like Siegfried achieves by his working of steel that same mastery over nature as do the engineers and craftsmen of industry. Steel is the raw material of 20th century industrial society, and the ability to produce and work iron marks a turning-point in the history of mankind. Steel fascinates us because in its reflection we see thousands of years of human history.

Wolf’s sculptures speak of this fascination. For him steel is not a random choice – he is not a sculptor who will choose his material from a variety of sources and then create his forms either in wood or bronze, or clay or stone. Both his choice of material and the manner in which he works it are intrinsic to his art. The relationship with steel is the cornerstone of his work – whether he works with a rusty surface or a highly polished one is determined by the piece in question. ‘Rust and polish are at the two ends of the same spectrum’, he says. Steel reacts with oxygen, which is only found on Earth. Rusting takes place naturally and leads to decomposition. Rust in a steel sculpture is like decline and decay in the life of humankind.

A polished steel surface, by contrast, is protected. The word ‘polish’ comes from Latin and means smooth, refined. Before a surface is polished it is raw and consists of troughs and peaks, whereas a polished substance is smooth. Its overall surface extent is therefore smaller, so oxygen has significantly less area on which to act. Moreover, polished steel reacts less strongly with oxygen and water.

Corrosion is a natural process; polishing is a human skill and is the most complicated, most exacting and most difficult art in metalworking. Even now, Samurai swords from a thousand years ago still show a visible polish, and in our own time Zeiss polishes the reflectors for giant telescopes. Polishing, whether of steel or glass, demands an endless amount of time, close work, energy input and expertise, nor can it be completely achieved – it can only ever be an approximation. Complete polishing belongs to the gods. If I stop the polishing and end this use of energy, then the surface of the steel will once again yield to rust. The difference between rust and polish in steel is the difference between nature and culture, between permanence and decay, and between aesthetic refinement and coarse superficiality.