Social constructionist analyses have a powerful, and influential, voice within the social science literature on technological risk. This paper recognises that the use of constructionist ideas has enriched debates about the social acceptability of technology, and moved them away from a narrow technocratic reductionism. However, we note that they have achieved these gains at the risk of losing track of the concrete features of technological artefacts. In seeking to include human sensibilities in the analysis, a preference has been given to theoretical conceptions of reality at the expense of engaging with what has been termed the signature of the technology: the specific ways in which it is articulated in practical reasoning and discourse within real-world settings. Here we use material on contrasting technologies, including some new data on nuclear fusion, to illustrate how these issues may be investigated empirically.