With reference to the Hansom piece "Dull metal jacket" about the National Centre for Popular Music in Sheffield (13 December, page 21), I believe that a response is required to explain why the building looks a "tad jaded".
Having been involved with the specification and supply of the stainless steel cladding material for this building, I can report that the staining is almost entirely caused by leachant from the black mastic sealant that was inserted between the individual panels and is not the result of any corrosion or tarnishing of the stainless steel cladding.

The original building design had gaps between the panels, with the water run-off behind the panels. During the building's construction, however, it was decided that a black sealant would be used to fill the 30 mm-wide gaps between the panels. It would appear that insufficient research was made into the properties of this sealant, as it soon became apparent that the black colour was leached out by "normal rainwater", causing the stains that are so evident on the exterior. Also, as there was no planned maintenance and cleaning programme for the exterior cladding, the building's facade now has more than four years of accumulated grime.

Postscript

Colin Honess, Corus, Rotherham.