In the 'black area' of the factory, enormous old dirty machines carry out a series of hot and noisy operations. Twenty-foot lengths of thin steel, already processed to the correct profile by the rolling mills at Darlington, are chopped into sections. A foot-operated press punches holes and slots for glazing bars and fittings and the frame sections are welded together in a shower of sparks. 'Most of the process is a simple one of heat and fusion,' says works manager Pat Hutchinson. In the mid-1930s, 180 welds an hour was champion; now it is 900. The smoking joints are sheared flat. 'This was probably done years ago by hand using a disc grinder.'
Hinges and handles, riveted into position in prewar days, are today welded. Glazing bars, though, are still levered in manually and hammered flush to the frame with a traditional windowmaker's hammer - its head long and narrow. Curved windows are made individually; the thin steel is passed through a set of rollers to form the distinctive shape. Originally, frames were simply painted with red oxide to inhibit rust. Today they are galvanised and specially coated.
There is one process, however, that cannot be supplanted by machine; it relies on the eye and skill of a pair of operators working together. Wielding 7lb copper hammers, they whack and tap - 'final' - each window to ensure that it is perfectly aligned and true. 'A good pair of final hands can do 480 windows a day,' says Pat Hutchinson. 'We've looked at mechanised methods, but without success.'
The period after the First World War brought an urgent need for cheap, mass-produced building materials. Crittall, by then a leading manufacturer, invented the Standard Metal Window specifically for the housing market, in many permutations of shape, size and style. To overcome resistance from architects, the company commissioned a dozen leading lights to design housing schemes using several of its styles, pressing home the message that the windows maximised light and air. Soon the Standard Metal Window featured in the new postwar housing estates and, by the end of the 1930s, in practically every home in burgeoning suburbia.
But Crittall's high profile today is not just to do with the quantity of windows supplied - although in its heyday the company had plants worldwide. More important was the fact that Crittall steel windows were embraced by leading 1930s architects. Those of the Modern Movement in particular, demanding as they did a new architecture based on industrialised materials, used them in celebrated buildings such as BBC Broadcasting House, the Art Deco former Daily Express building in Fleet Street, and Lubetkin's Finsbury Health Centre - just as Frank Lloyd Wright did in Falling Water, the house he built at Bear Run, Pennsylvania.
Crittall is at Springwood Drive, Braintree, Essex CM7 7YN
(tel 0376 324106).