In this article I set out some of the distinct ways materials and components are described in architectural specifications. In many cases, as we might expect, materials are simply named, albeit in a great variety of ways from brand name to botanical species. In others, materials are specified via a reference to something else – to be built ‘like is the timbers of the Rente of Robert’, or to match a sample of stock bricks ‘marked No 1 to be seen with the Architect at No 1 Westminster Chambers’. We find many examples of what Bertrand Gille has called the ‘recipe’ – details about the ingredients and processes of making up a material or fixing it in site (Gille locates one in Vitruvius). And recently, and ever more pervasively, materials are prescribed in terms of their performance – how they are to behave in the finished building, whether acoustically or structurally or thermally and so on, with no mention at all of how the result is to be achieved. Indeed, the point may be precisely to avoid naming a particular material so that the responsibility for a compliant selection no longer rests with the architect. These descriptions, with their language of properties and materials science, could not be more different from the instructive prose-like sentences of the process-based specification. With one describing how to make up a given material, and the other how it is to behave, we might also suggest that they depend on very different, even incompatible, conceptualisations of the material – as artefact on the one hand and as actor on the other.

Differences between types of clause are recognised in contemporary technical literature and guides to specification practice, although the distinctions considered significant vary greatly. The typologies set out here, however, are drawn from my own survey of documents from the eighteenth century to the present day. In some cases, such as the performance clause, the type I identify maps directly onto a widely used industry category but in others, such as the process-based clause not so much in use today, it may only share some similarities with existing technical definitions.