Daguerreotype Process

The Daguerreotype was the World's first practical photographic system. The process was invented by French artist & scientist Louis Daguerre over a long period between 1821-1837. The rights to use Daguerre's process were bought by the French government in 1839 and "given free to the World".

The Images

The Daguerreotype is a positive image made on a metal plate. Each image is made by a separate exposure in the camera.

The process

There are five stages in making a Daguerreotype:

1. Plate Preparation: a copper sheet was plated with silver (by Sheffield plating, or, later, by electroplating; this is then polished to a very high gloss
2. Sensitisation: the plate is placed in an iodizing box and exposed to iodine vapour until all the surface silver has been converted to silver iodide, turning the plate orange. This is the light-sensitive coating. This had to be done shortly before the exposure.
3. Exposure: The plate is loaded into a camera, and an exposure made simply by removing the lens cap. Exposures in early cameras could be over twenty minutes, even in bright daylight! However, this was less than some other, earlier processes. In 1840, Englishman John Goddard showed that sensitivity could be increased by using bromine, as well as iodine; this, together with improving lens technology brought this down considerably. Petzval's lens in particular brought typical apertures down from ~f14 to ~f3.5 - four stops, or 16 times shorter exposures.
4. Development: the plates are fixed over a bath of mercury, which is heated to 60°C (140°F); mercury vapour forms an amalgam with the exposed silver iodide.
5. Fixing: unexposed silver, not amalgamated with mercury, is washed off the plate using a salt (sodium chloride) solution (later replaced by weak sodium thiosulphate solution). This leaves the mercury/silver amalgam as a permanent - but delicate - image. This image would sometimes be toned with gold chloride. The plate was usually mounted in a glass-fronted frame to protect the fragile surface from being scratched off, or oxidising (tarnishing to black, as silver cutlery does) in the air.

Disadvantages

The Daguerreotype had several problems:

• There was no negative; individual exposure only made one Daguerreotype - copies or enlargements were not possible except by photographing a new, inferior, Daguerreotype of the original. Some Daguerreotypes were engraved to make printing plates.
• Long - or very long - exposure times - made sharp images of people almost impossible with early lenses & plates.
• The photograph had to be viewed in good light, and carefully angled to be seen well; viewing at the wrong angle made the image appear as a negative.
• Since the plates were not transparent, the image is viewed from the same side as the lens - so the picture is normally left-right reversed. Some cameras incorporated a mirror to correct this during exposure - but most Daguerreotypes are "mirror images".
• The silver plates and processing (and the individual exposure/processing cycle for each picture) were expensive.
• The process involved highly poisonous bromine & mercury vapours.

However, in spite of these drawbacks, Daguerreotypes were popular and the process spread across the world. One exception was in the British Empire; whilst the French government had given rights to the World, the Daguerreotype had been patented in Britain and hence it's colonies - which encouraged use of many other processes.

Daguerreotype photography continued until the late 1850s - particularly in France - until largely replaced by the wet-collodion (Ambrotype) process.

Sources

• The Focal Encyclopedia of Photography, Focal Press/Elsevier, 4th ed., 2007
• Coe, Brian, Cameras, from Daguerreotypes to Instant Pictures, Norbok, 1978

Links

• The Daguerre Society has Daguerreotypes and history
• The Daguerreotype by Robert Leggat

[[Category: Daguerreotype camera|*]