Appeared earlier in the IACIS Newsletter 48 of October 2011.
While preparing a manuscript on high yield synthesis of uniform gold nanoparticles, a discussion on the stability time scale of colloidal dispersions developed in which it seemed appropriate to mention the world record in this: the more than 150 year stability of the gold sols prepared by Michael Faraday. In 1856 Faraday turned his attention to the interaction between light and matter after noticing that very thin films of gold kept the shiny yellow reflection but transmitted green light. He made numerous samples of colloidal gold of which he learned how to obtain the various colors as well as how to make them stable. In 1857 this work was described in the Bakerian lecture to the Royal Society. Many of these samples are lost but according to common knowledge, some of them remain in London.
For the manuscript at hand, a primary source was needed to refer to but whatever we could find; they were all – at best – secondary sources: information collected by others. One of the more explicit sources, the website of a well known manufacturer of colloid scientific equipment, mentions the Science Museum in London. Many other sites and documents do likewise.
After sending an electronic request to the conservator of the museum, the following answer was received “The situation is a little bit complex. Until 1999 we had a Faraday exhibit which displayed gold films deposited on watch glasses made by Faraday alongside a tall vessel containing colloidal gold (Zsigmondy’s method) which otherwise had nothing to do with Faraday.” The interesting consequence of this statement by the conservator of the Science Museum could be that there are quite a few false statements about and very likely even pictures of vessels not older than a few years instead of the 155 as claimed!
A further message from the conservator of the Science Museum reveals that some gold sols, of which pictures circulate the internet, could be in the Royal Institution (Ri), also in London. The confirmation came from the Curator of Collections who stated that “They are on permanent display within the Michael Faraday Museum area of the Ri, on the lower ground floor of the building, within the only section of Faraday’s original laboratory that still exists.” In addition, pictures were sent of which one accompanies this article and demonstrates the Tyndall effect that betrays colloidal dispersions.
In conclusion, the gold sols made by Faraday are indeed in London but not in the often mentioned Science museum but in the museum of the Royal Institution. We are happy to have spent some time finding out the truth about these gold sols and not to have merely repeated a false statement.