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Discovering Discovery:
How Faraday Found the
First Metallic Colloid
Ryan D. Tweney
Bowling Green State University
In 1856, Michael Faraday (1791–1867) conducted nearly a year’s worth
of research on the optical properties of gold, in the course of which he discov-
ered the ªrst metallic colloids. Following our own discovery of hundreds of
the specimens prepared by Faraday for this research, the present paper de-
scribes the cognitive role of these “epistemic artifacts” in the dynamics of Far-
aday’s research practices. Analysis of the specimens, Faraday’s Diary records,
and replications of selected procedures (partly to replace missing kinds of spec-
imens and partly to understand the “tacit knowledge” implicated in Fara-
day’s research) are outlined, and a reconstruction of the events surrounding
the initial discovery of metallic colloids is presented.
In an 1852 lecture before a general audience at the Royal Institution,
Michael Faraday (1791–1867) demonstrated a fascinating property of me-
tallic gold: In contrast to all other metals, “Gold has been beaten into
leaves so ªne as to become partially transparent,—not in consequence of
any cracks, holes, or ªssures, but by the shining of light through its sub-
stance” (Faraday 1853, p. 69). To illustrate his point, Faraday appears to
have used a large gold leaf, about 3 square, mounted on a glass plate 6
square; the actual leaf still survives in the collections of the Royal Institu-
I thank Frank James and the staff of the Royal Institution of Great Britain for unparalleled
assistance! The early work on this project was supported in part by the British Academy of
Arts & Sciences and by NSF STS Award #0100112. Lawrence Principe was generous with
his time in aiding our replications and helping us navigate the tricky safety and handling
issues that arose in some of the chemistry. Many others have devoted time and energy to
various aspects of this project, including Chris Ayala, Neal Berg, Harry Brown, Robert
Gibby, Ryan Mears, Christiane Spitzmüller, Yanlong Sun, and Andy Wickiser. Elizabeth
Cavicchi, David Gooding, and two reviewers provided deep readings of an early draft of
this paper. Discussions with Elke Kurz-Milcke helped throughout the endeavor.
Perspectives on Science 2006, vol. 14, no. 1
©2006 by The Massachusetts Institute of Technology