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Ambrotype is a photographic process resulting in positives on glass, originated by Frederick Scott Archer and Peter W Fry in 1851[1]. It was intended as a cheaper alternative to the Daguerreotype. It is based on the wet-collodion process. It was also known, in Britain, as "collodion positive".

Glass plates are prepared, and developed as in the wet-collodion process, but underexposed. This gives a less dark glass negative. The negative is treated with mercuric bichloride to whiten the exposed areas. The plate is mounted in a metal frame with a black background. The background makes the negative appear positive - as the whitened silvered areas reflect light, and the transparent areas show the black background.

The back was sometimes varnished or coated with balsam to improve the image; James Ambrose Cutting of Boston was granted a US patent in 1854[2] on a method of doing this - which makes the image "greatly increased in strength and beauty by imparting additional brilliancy", while also protecting the silver image with a glass backing.

Ambrotypes were often hand-tinted to increase the contrast; without this, Ambrotypes are grayish-white and compare poorly to Daguerreotypes.


  1. Focal Encyclopedia of Photography, Focal Press, 1976 edition, p.40
  2. US Patent 11,267 of 1854, Improvement in Photographic Pictures on Glass, granted to James A. Cutting; at Espacenet.