A wall is never only a wall. Over the course of a day it becomes a sundial, a screen, a calendar. The same plane of concrete reads as cold and blue at nine in the morning and as warm and almost soft at six in the evening. When we choose a material, we are really choosing how a building will record time.

This is why we rarely specify a material from a sample. We build a mock-up on site, at full scale, and we look at it for a week. A limestone that seemed too yellow in the studio can turn perfectly neutral under a north sky; a concrete that looked refined under artificial light can appear lifeless when the sun moves across it.

Texture is a function of light

Raking light reveals every irregularity in a surface. A board-marked concrete wall that is barely legible at midday becomes a field of lines when the sun drops to fifteen degrees. We use this deliberately: in the Saline Gallery, the walls of the long gallery are smooth, because its light is even; in the stair halls, where light falls steeply from above, the walls are textured so that the light has something to describe.

The opposite is also true. In a dim room, a highly textured material becomes visual noise. Darker rooms ask for quieter surfaces and more reflective finishes — honed rather than split stone, oiled rather than raw timber.

None of this is new. Every vernacular builder knew it. What has changed is that most contemporary construction is designed on screens under constant artificial light, and most materials are chosen from catalogues. Returning to the site, and to the hour of the day, is the simplest way we know to make a building better.

We are not choosing a material. We are choosing how a building will record time.

For the studio, this has become a method. Every material study begins with a question about light — where it comes from, at what angle, at what time — and only then turns to colour, finish and cost.