The roofs are serrated, like a saw. Around Honcho in Kiryu, weaving mills with sawtooth roofs and brick storehouses stand scattered through the ordinary town rather than gathered into a compound. The shape has a reason: the vertical face of each tooth is glazed and faces north, which gives a steady light that does not swing with the sun, and steady light is what you need to judge the colour of thread. Get that judgement wrong and a whole bolt is wrong with it. The district was designated a preservation area in 2012, on the strength of a shape that was never meant to be admired.

A number of the buildings now hold workshops and cafes. The machinery has gone and the floors it stood on have not, so the new tenants have inherited wide, low-columned spaces built to a loom's dimensions — high enough for shafts, clear enough for rows — and are using them for things nobody had in mind. The city has a population in the hundred thousands, Takasaki is about fifty minutes away on the Ryomo line, and finding uses for empty mills is an ongoing local occupation rather than a completed project. Some buildings are waiting; a few will not be saved, and the ones that are tend to be saved by somebody who needed a big room cheaply.

A shape chosen for light is now liked for its atmosphere. North-facing glass was a solution to a problem — how to see a colour correctly at four in the afternoon in November — and had nothing to do with taste. Photographing the sawtooth, you are photographing not a style but somebody's need to tell one shade of thread from another.