A fortunate accident supposedly occurred, when a briefly exposed plate was taken from the camera and placed in a drawer for later use was found to have produced a visible image. Daguerre apparently experimented with various chemicals present in the drawer, eliminating them, before finding that the development was caused by mercury from a broken thermometer.
Daguerre also found that the images could be 'fixed' or made more or less permanent, by bathing the exposed plate with its image in a strong solution of sodium chloride (salt) until the yellow colour of the silver iodide disappeared as it dissolved in the salt.
Daguerre interested the French government in the process, and presented it to the French nation in exchange for a pension. He also took out a patent in England, so he could exploit his invention commercially there, as well as working with others to market 'Daguerre' cameras and other equipment in France and across the world. His manual of the process was published very shortly after his first public demonstration.
There were soon improved versions of his process, including the use of bromine (J F Goddard, 1840) and chlorine (A Claudet, 1841) as well as iodine to produce the light sensitive silver salts on the plate surface (silver bromide and silver iodide respectively.) These made the plate more sensitive to light, and together with faster lenses made it possible to reduce exposures from the 5-30 minutes used by Daguerre down to 5-30 seconds.
Sir John Herschel, the British scientist best known as an astronomer, heard the news of Daguerre's process (and had also seen some of William Henry Fox Talbot's early 'photogenic drawings') 3 weeks after it was announced. He immediately set to work - without knowing the details of either process - and in a week had managed to produce his own photographic images, in a way similar to Talbot. Herschel made one great improvement, that was taken up immediately by Daguerre when he learnt of it. Both Talbot and Daguerre had used a strong common salt (sodium chloride) solution, to 'fix' their images, but it was not very effective. Herschel had 20 years earlier discovered that 'hyposulphite of soda' (now called sodium thiosulphate) was effective in dissolving silver chloride and bromide, and used that to fix his images. Daguerre was quick to adopt this new method for his process, and Talbot slowly followed. Generations of photographers have used 'hypo' since that time.
Gold toning, introduced by Hippolyte Fizeau in 1840, soon became normal practice, as it intensified the images and gave them a greater brilliancy. It also created more permanent images that tarnished less rapidly.
Also in 1840, Alexandre Edmund Becquerel found that exposed daguerreotype plates could be developed without the use of mercury, simply by exposure to visible light. To prevent fogging of the plates it was necessary to completely exclude the wavelengths in the ultraviolet (and possibly blue) regions of the spectrum. This is most easily done by using a deep red filter for the development exposure. Although this method seems to have been put to little practical use at the time, with our increased recognition of the health hazards of mercury vapour it is now used by most contemporary practioners of the process.
The English patent taken out by Daguerre meant that the use of the process was restricted to a few licensed portrait studios in England, but elsewhere, particularly in France and America, the use of the process developed rapidly. It was particularly suited to studio portraiture, although the long exposures - usually from 30 seconds to several minutes - made sitting quite an ordeal. However, processing times using mercury development were relatively short, and because the light sensitive material was just an incredibly thin layer on a metal surface, only brief washing etc was needed. By the time the sitters had recovered from the ordeal - perhaps with a cup of tea or something
stronger - they could be presented with the case containing their likeness.
The detail in the images was limited largely by subject movement and lens performance. For portraiture, wide apertures were a priority, and some distortion and lack of resolution towards the edges of the image was acceptable. For landscape and architecture, slower 'rectilinear' lenses giving low distortion and high resolution across the plate was needed.
Many daguerreotypes were hand-coloured, a practice probably introduced by Johann Baptist Isenring in Switzerland.
The daguerreotype was the main process in use in commercial photography from 1839 to the early 1850s, and literally millions of daguerreotype portraits were made. The collodion (wet plate) process generally replaced it very rapidly, as it allowed multiple copies of images to be made. There were also no patents on this process, allowing its rapid adoption.
The American daguerreotypists were noted for the quality of their work and daguerreotypes continued to be important until around 1860 there, the rapid nature of the process without the need for printing being important. However, similarly rapid direct positive processes based on wet collodion, such as the tintype, soon replaced them for cheaper work because the iron plates used for this were considerably cheaper than silver-coated copper."
["_notes_technical_details"]=>
string(3589) "In the early years, most daguerreotypes were made on a mechanically produced silver coated copper plate, manufactured by rolling out a copper ingot with a layer of silver soldered to it. Later it became more normal to deposit silver by electrolysis on a carefully polished copper plate - this could be cut to the size required before plating. The following steps were then needed.
1. The silvered plate was cleaned with dilute nitric acid and carefully polished to remove all surface irregularities. The superior quality of US daguerreotypes was due to better polishing methods, including the use of machines.
2. The plate was then placed in a closed box with the silvered side a few inches above a layer of iodine crystals. A layer of muslin was sometimes placed between them to ensure even dispersion of the iodine vapour. For faster plates, a similar treatment with bromine or chlorine was given, usually after an initial exposure to iodine, and was followed by further exposure to iodine.
The process can be monitored visually in dim light. The iodine reacts with the silver metal to form silver iodide as a very fine layer. With continued exposure, this layer gets thicker, and as it does so, the colour of the plate changes, at first yellow, then orange and red and blue, before going back to yellow again and repeating the series of colour changes. As the layer thickens, the contrast of the plate reduces. The sensitivity to light is greatest at the yellow stage, decreasing to blue, and then increasing again as the plate returns to yellow. So the plate is usually used at the second or third time it becomes yellow.
3. The plate is placed in the camera and exposed for a time depending on the lens aperture, subject and lighting (and whether bromine or chlorine have been used to accelerate the process.) If a correct way round image is needed, a mirror is used in front of the lens, adding slightly to the exposure needed.
4. The plate was taken out of the camera in a dimly lit room and put into a developing box. Normally the plate was held at 45 degrees a few inches above a bath of mercury, heated by a small spirit lamp to around 60 C. A glass window in the side of the box enabled the development to be viewed - it was normally for around 20 minutes.
5. The plate was rinsed for a second in filtered rainwater, then immersed in a sodium thiosulphate solution until the yellow colour had completely disappeared (modern workers may like to fix for twice this clearing time.) It was then washed and dried. Gold toning was usually carried out by adding gold solution to the sodium thiosulphate fixer, or it could be done immediately after fixing, with just a brief rinse between the two baths.
6. If the daguerreotype was to be coloured, this was then done either by dusting on extremely finely powdered dry colours with a fine brush, or sometimes weaker colours might be produced by using solutions of the colour in alcohol. The colours mainly used were gold, carmine, chrome yellow and ultramarine, and they were mixed to produce other colours.
7. A metal or card overmat was then placed on the plate, with a sheet of fine glass on top. The overmat prevented contact between glass and plate. The edges were often sealed with tape before placing the image in a suitable case. Many cases were hinged to protect the image, and often had a dark velvet lining on the cover, which could help in viewing the image if held at the correct angle."
["_notes_preservation"]=>
string(541) "Daguerreotypes can be restored by skilled conservators, although this may not always be advisable, as the images are very fragile and there is always some risk of damage.
Preservation can be aided by the replacement of the matt and glass. However, the original glass contributes to the look of the object and is often retained. Layers of clear mylar can be used between matt and glass and behind the plate, together with improved sealing. The Library of Congress web site (see Resources) gives some detail on their approach."
["_notes_summary"]=>
string(1672) "
The Daguerreotype was the first practical photographic process.
Invented by Daguerre in the 1830s and announced to the public in 1839.
It was made using a copper plate, coated with a thin layer of silver.
A positive image becomes visible on the plate after the development process.
The images have to be viewed correctly for the image to appear as positive.
The image is physically fragile and tarnishes rapidly due to pollutants in air - they were sealed behind glass (with a thin brass or similar metal matt as a spacer), and usually put in a frame or case immediately after production.
The camera produces a single image, and daguerreotypes are not easily reproducible.
The image is highly detailed with and can reproduce a delicate range of tones.
Unless exposed using a mirror in front of the camera lens, they are a reversed image of the subject.
The great majority of vintage daguerreotypes were portraits of single individuals - other subjects are rare. Usually these are three quarter length or simply heads and shoulders.
Colour was added to some daguerreotypes by hand, usually with finely ground pigment on a dry brush. Tarnishing can also sometimes give various colours to parts of the image.
Most daguerreotypes are small images - generally fractions made by cutting the 'whole plate' size of 6.5 x 8.5 inches into 4, 6, 9 or 16 smaller plates before use; (1/16 plate images are around 1" x 2".)
Daguerreotypes were used in commercial photography from around 1840 to 1855 in Europe, and until around 1860 in the USA.
"
["_notes_photographers_of_note"]=>
string(1640) "Daguerreotypes needed to be encased behind glass and did not lend themselves to direct publication, although many attempts were made to process them to enable them to be used as printing plates. The greatest of the early publications based on them was undoubtedly the 'Excursions daguerriennes' (1840-1844) of Noël-Marie Paymal Lerebours. Several of the plates used for this were produced using an etching process developed by Armand Hippolyte Louis Fizeau (1819-1896), but the plates still required extensive retouching by hand. The other plates used in the work, and almost all other published works from daguerreotypes were made either by direct hand engraving onto a daguerreotype plate, or, more usually, by tracing the image onto a copper plate that was manually engraved.
Daguerre
Dr John W Draper
Samuel F B Morse
Alexander S Wolcott (Wolcott & Johnson)
Albert Sands Southworth & Josiah Johnson Hawes
Matthew B Brady
Edward Anthony
William & Frederick Langenheim
John Jabez Edwin Mayall
Richard Beard
William Edward Kilburn
Cornelius Jabez Hughes
Antoine Claudet
N. M. P. Lerebours
Horace Vernet
Frederic Goupil Fesquet
Joseph Philibert Girault de Prangey
Freidrich Martens
Bisson Freres
Herman Biow
Carl Ferdinand Stelzner
Johann Baptist Isenring"
["_notes_current_use"]=>
string(951) "There has been a considerable revival in the process in recent years, although the number of workers is still relatively small, due to the rather tricky nature of the process. Considerable experience is needed to produce consistent results.
Modern workers have the advantage of exposure meters to gauge exposure, although the readings need to be extrapolated due to the low speed of the material. The meters also measure all visible light, while the daguerreotype is only sensitive to ultraviolet and a part of the blue region.
Most modern workers use Becquerel development to avoid the safety hazard of hot mercury, mercury vapour being a dangerous cumulative poison. A convenient approach is to carry this out in the darkslide, covering the aperture with a sheet of rubylith (deep red) film, and pulling out the darkslide. In sunlight, a properly exposed plate will develop in around 15-25 minutes with this method."
["_notes_identification"]=>
string(0) ""
["_notes_possible_confusion"]=>
string(351) "Daguerreotypes have a unique appearance and are seldom confused with other processes.
Images made using the direct positive collodion processes, either on metal plates (tintype / ferrotype) or glass (ambrotype) may sometimes be found in similar cases. The images are much duller when compared to daguerreotypes, and are easier to view"
["_notes_thanks"]=>
string(14) "Peter Marshall"
["_exhibition"]=>
string(0) ""
["_catcode"]=>
string(3) "687"
["_image_ids"]=>
string(34) ":11400:11413:6945:11229:7496:7982:"
}
}
