A collodion positive (ambrotype) of three men, taken at the studio of William Nichols, Cambridge. The smartly dressed men are photographed against a painted backdrop designed to look like a library or study. The collodion positive process (also commonly known as ambrotype) was popular during the 1850s and 1860s. An underexposed collodion negative on glass was backed with a black opaque coating to create a unique positive image.
© National Museum of Science & Media / Science & Society Picture Library