Ryan D. Tweney has been working with Michael Faraday's slide specimens, prepared as part of his 1856 researches on the colors of gold. Photographs of all of his specimens have now been placed on a web site: http://aveburybooks.com/faraday/catalog.html
A paper detailing a cognitive analysis of his work is linked on the web site, and may be accessed directly at:

http://www.aveburybooks.com/faraday/discovering_discovery.pdf