Abstract This paper follows the history of an object. The purpose of doing so is to come to terms with a distinctive kind of research object ? which we are calling a ?test object? ? as well as to chronicle a significant line of research and technology development associated with the broader nanoscience/nanotechnology movement. A test object is one of a family of epistemic things that makes up the material culture of laboratory science. Depending upon the case, it can have variable shadings of practical, mathematical and epistemic significance. Clear cases of test objects have highly regular and reproducible visible properties that can be used for testing instruments and training novices. The test object featured in this paper is the silicon (111) 7?7, a particular surface configuration (or, as it is often called, a ?reconstruction?) of silicon atoms. Research on this object over a period of several decades has been closely bound up with the development of novel instruments for visualizing atomic structures. Despite having little direct commercial value, the Si(111) 7?7 also has been a focal object for the formation of a research community bridging industry and academia. It exhibits a complex structure that became a sustained focus of observation and modelling. Our study follows shifts in the epistemic status of the Si(111) 7?7, and uses it to re-examine familiar conceptions of representation and observation in the history, philosophy and social study of science.