Metalwork

Corten is not rust left to its own devices. It is a weathering steel: its oxide layer bonds to the metal and slows corrosion instead of feeding it. For that it needs an alternation of wet and dry; set under cover, sheltered from the rain, it stays orange and powdery instead of stabilising. The patina settles within one to three years depending on exposure, and we work in thick sheet, because a few tenths of a millimetre are lost along the way.

Stainless, for its part, is chosen. Grade 304 holds up perfectly well in a garden here; 316, which costs more, is justified beside a swimming pool, near a store of road salt or in a chlorinated atmosphere. After welding, the beads are pickled and passivated: the rust coloured streaks seen on a lot of metalwork nearly always come from that, or from ordinary steel dust left by a grinder working nearby.

On painted or galvanised steel, a weld is paid for twice: stripping back before, restoring the zinc and the paint after, failing which the rust starts again from the bead by the second winter. That is why we prefer to draw the whole piece before cutting rather than extend a gate on site. And we say so when metal is not the right answer: to screen yourself from a neighbour, a hedge costs less and does the job better within three years.