Ambrotype
A photographic image on glass where a positive print was produced without the need to print from a negative. An underexposed and then developed collodion negative on glass, when backed with an opaque coating such as black lacquer, appeared as a positive image. The process was developed in 1852 and promoted by commercial studios as a cheap alternative to daguerreotypes and was used mostly for portraiture.
Derwent Coleridge; Mary Coleridge (née Pridham)
by Unknown photographer
1856
NPG P322
Barbara Leigh Smith Bodichon
by 'Holmes of New York'
1857 or 1858
NPG P137
Sir Joseph Nias
by Unknown photographer
NPG P2
Luke Howard; John Eliot Howard (right)
by Unknown photographer
circa 1855-1860
NPG P784