Submitted by Al …
(Adapted from The Encyclopedia of Photography ©1963)
The year 1839 was one of the most important in photographic history, because it saw the introduction of two different processes; the daguerreotype of Louis Daguerre and Nicephore Niepce, and the calotype of Henry Fox Talbot.
At first the daguerreotype was extremely popular, practiced by many amateurs, and a great source of revenue for many professionals. It gradually lost favour following the introduction of the collodion and other faster photographic processes of the 1850s.
Much has been written about the daguerreotype. Even so, very few people are able to distinguish one from a tintype or an ambrotype. There is no superficial distinguishing mark since all three were usually put in the same kind of case or frame. The difference is to be found in the process itself. The daguerreotype is a mirror-like picture which, for proper viewing, has to be adjusted to one’s
eye in relation to the source of light, ridding it of reflections. Without the photograph, the plate is just a mirror of polished silver.
The ambrotype, a later development about 1855, was made on glass and backed by black velvet or paint and may be viewed from almost any angle.
With the tintype, the picture is on a ferrotype, a thin enameled sheet of iron which generally resembles tin, and so was given its popular name. It may be viewed as any present day photograph.
THE DAGUERREOTYPE PROCESS
During the 1830s in France, Daguerre was experimenting with his photographic process – an attempt to make the image cast by a camera obscura into a permanent one. At the same time another Frenchman, Joseph Nicephore Niepce, was working on a similar process, called heliography. The two eventually formed a partnership and collaborated on the experiments with the result that on August 19, 1839, a workable photographic process was presented to the public at a joint meeting of the French Academy of Sciences and the Academy of Fine Arts.
The daguerreotype process as practiced around 1950 was briefly:
Preparing the plate. A copper plate was silvered on one side either by rolling a thin silver plate into contact, or by galvanic plating. This silver layer was highly polished.
Sensitizing the plate. The silvered copper plate was placed inside a box filled with iodine vapour. Next, the plate was moved to a box where bromine vapour was deposited (this step was introduced in later years to increase sensitivity). Finally, it was treated again with iodine vapour.
Exposure. Exposure in the camera took place immediately after sensitizing, with the exposure varying from three to 40 minutes.
Development. The image of a daguerreotype was latent, unless extreme over-exposure occurred, and it had to be developed for two or three minutes in a box filled with mercury fumes. Mercury particles were deposited in proportion to the exposure received by the iodine of silver. The dark portions of the image (unaltered iodide) were removed by the fixing.
Fixing. The image was fixed when a solution of hyposulfite of soda was poured onto the surface for a few seconds. A washing in distilled water followed.
Toning. The image was then toned with a mixture of hyposulfite of soda and chloride of gold – with the plate held over a flame during the toning. The daguerreotype was then washed again in water, and dried over a flame.
The finished picture. The final image – always reversed, unless a correcting prism was used over the camera lens, was covered with glass and usually bound in an ornate leather case. While highlights of the image were represented by varying deposits of mercury, the shadows were more or less the clear polished silver of the basic plate. Thus the daguerreotype has a mirror-like effect and is best viewed when turned away from direct light.
COPYING THE DAGUERREOTYPE
To make a good copy of a daguerreotype showing its rich quality to best advantage, remember that you are photographing an image on silvered copper, a virtual mirror. The camera must be placed directly in from of the daguerreotype so that the result will be free of lateral distortion, however, the camera itself must not be reflected in the daguerreotype.
Place in front of your camera a board with a hole in the centre, cut to the size of the camera lens. On the side facing the daguerreotype, cover the surface with black felt or velvet. Next, aim a standard floodlamp from either side at such an angle that no reflections can be seen while focusing on the groundglass or viewer. Take a meter reading and make three separate exposures, one as indicated, one at a stop over, and one at a stop under. After development, it will be possible to decide on the best exposure for the final negative. Carry out this procedure in a reasonably darkened room with no lights other than the two you are using.
PRESERVATION
It is common belief that daguerreotypes should be kept in dark places to prevent them from fading. Some experts do not believe that the intensity of light has a damaging effect, but all agree that heat does cause condensation of moisture that tarnishes the silver plate which is the base of a daguerreotype. Therefore, a dry, even temperature is the best preservative for daguerreotypes, and under these conditions they can be exhibited without fear of fading.
RESTORING A DAGUERREOTYPE
To clean the tarnish from a daguerreotype, its surface must never be touched, or it will rub off or scratch beyond repair. Always remember that nothing but liquids must touch the picture surface.
The following procedure is recommended:
Carefully remove the daguerreotype from its metal binding frame.
Next, remove the binding tape which holds the glass and brass matte in place.
Now lift out the daguerreotype (do not slide it) and place it face up in a clean tray of water for about ten minutes. Repeat this in clean water until all particles of dirt have been soaked loose.
Rinse under a tap of water so that particles of dirt may flow off.
While this soaking process is going on, make a solution of potassium cyanide, 10 grains for each ounce of water used. Keep pouring this solution over the daguerreotype until it is clean. Caution: Potassium cyanide is a deadly poison – do not use if you have cuts in your hands.
Wash all trays and throw away unused solution when finished.
Wash the daguerreotype in distilled water until it is free of cyanide.
Then hold the daguerreotype at one corner with a pair of pliers and dry evenly from the top downward over a Bunsen burner or an alcohol lamp.
If any water marks should remain, allow the daguerreotype to cool, and then rinse it again in distilled water and dry as before.
After the cleaning is finished, wash and dry the protecting glass and assemble it as it was originally. Then bind it together with plastic tape and return it to its frame.
댓글