Everything we make begins as a full-size drawing on brown paper — the cartoon — over which every piece of glass is cut in turn. Nothing about that sequence has changed since the thirteenth century, and there is no version of it that can be hurried.

Paint is vitreous: ground glass, iron oxide and gum arabic, laid on wet and then fired at around 640°C until it fuses into the surface. It cannot be undone. A badly judged trace line means cutting the piece again and starting it over.

Leading is the last quiet fortnight of a job. The came is stretched to take the spring out of it, cut and shaped around each quarry, then soldered at every joint on both faces, cemented, and whitened.

A window leaded properly will stand for a century before it needs releading. One leaded badly will bow within twenty years, and no amount of good painting will save it.