A selection of images from the Library of Congress found via the always excellent Ptak Science Books blog. The daguerreotype, invented by Louis-Jacques-Mandé Daguerre in 1837, was the first commercially successful photographic process and was popular throughout the mid-19th century. Daguerreotype portraits were made by the model posing (often with head fixed in place with a clamp to keep it still the few minutes required) before an exposed light-sensitive silvered copper plate, which was then developed by mercury fumes and fixed with salts. This fixing however was far from permanent - like the people they captured the images too were subject to change and decay. They were extremely sensitive to scratches, dust, hair, etc, and particularly the rubbing of the glass cover if the glue holding it in place deteriorated. As well as rubbing, the glass itself can also deteriorate and bubbles of solvent explode upon the image. The daguerreotypes below are from the studio of Mathew Brady, one of the most celebrated 19th-century American photographers, best known for his portraits of celebrities and his documentation of the American Civil War which earned him the title of "father of photojournalism". The Library of Congress received the majority of the Brady daguerreotypes as a gift from the Army War College in 1920.