PRESERVATION OF OLD DOCUMENTS (II)
Light creates the images. But the light also destroys them.
The photographs' procedures of preservation are very similar as those of the papers: low temperature, low humidity; both of them must be stable. Photos need to be stored in dark places, few exposed to the light; and if it's possible, never to the daylight. In ventilated rooms, clean, without dust, filed in albums or in acid free containers.
How many different kinds of photographs are conserved in museums, libraries, or households?
Photographs exist since approximately 1840. But the first photos were essentially different of the current ones. At the beginning they were supported in metal, not in paper. The first popular photos at the half of the 19th century were daguerreotypes.
METAL SUPPORTED PHOTOGRAPHS
A daguerreotype is a copper plate, covered with a thin coat of an amalgame of silver and mercury, and sometimes gold. On this plate is printed by photochemical process a neat monochromatic image. The capture of this image is direct, it means, a daguerreotype is a positive image, a unique image. The image is mirror-like, laterally reversed from its original position; letters and numbers will be seen reversed. Being well conserved, its surface is shiny like a mirror. When viewing the images by certain angles, they could be seen either as positives or negatives. The original, -unique- is conserved protected by a glass, a few milimeters separed from the plate, all sealed by a brass strip, and mounted in a wooden or leather case. That was the way they were originally presented. They were used between 1840 and 1860. Initially the exposure time was a long period between 5 and 20 minutes, until 1855, when those times were shorten to 10 seconds, using bromide as well as iodone to sensitise plates, and also increasing the lens' sensitivity.
The daguerrotype was invented by Nicéphore Niépce, who achieved, since 1826, different forms of photographed images. In 1829 he signed an agreement with a painter and theatrical scenographer, Louis Daguerre, for 10 years, to work on photography investigation together. In 1833 Niépce died and Daguerre followed up with the works on photography, improving the system, and presenting it in 1839 to the French Academy of Sciences. He received a patent on the invention from the French government.
Daguerreotypes must be conserved into their original cases, with their glass protection. In the case of not having the glasses, they must be sealed between two pieces of glass separed 1 or 2 milimeters from the plate. The silver plate should not be touched with fingers, because it's extremely sensitive; it's recommended to handle it with cotton gloves. Daguerreotypes need to be stored in cardboard boxes acid free, with a neutral degree of acidity, like ph7. Temperature must be between 60 and 70 degrees and humidity between 35 y 50%. For exposition, it's recommended the incandescent light between 50 and 75 luxes.
AMBROTYPES AND FERROTYPES
Daguerreotypes had a high cost of production and some danger when processed, because of the highly toxic emanations of mercury. Other safer and cheaper supports were investigated.
Ambrotypes were made on glass plates and they lasted very short time. Only until 1865. The image is formed on a wet colodium emulsion (a solution of cotton, nitric and sulfuric acid, dissolved in ether) covered with silver, to make it more sensitive.
Ferrotypes, also called Tintypes, as they were inexpensive, were used up to the first years of the 20th century, more or less until1915. It was a variation on the wet colodium process, using as support of the image a sheet of iron blackened by painting or laquering. They produced plain images, of grayish tones and with low contrast. Sometimes they were varnished, to protect the image and to make them more brilliant.
Both photographs, ambrotypes and ferrotypes result, like daguerreotypes, in only positive images, and mirror-like, laterally reversed. (See soldier's hat in the picture above).
Photographers hardly were trying to get multiple copies from a positive image. Until then the only success was the calotype, (invented by Henry Fox Talbot in 1840 and patented by him) which allowed to get positives by contact with paper, but they had a very poor quality, because the process was made with the current writing paper. Paper imperfection's were transmitted to the images. It couldn't supplant daguerreotypes, because of its low quality images. The problem was to get a homogenic surface, but they couldn't find the chemical products to obtain it. A photography printer, Louis Désiré Blanquard, solves the problem, near 1850: coating the sheets of paper with salted egg white snow shaked, creating a shiny surface; this layer was sensitised with a solution of silver nitrate and the silver salts didn't reach to contact the paper fibers, obtaining a very high definition image. Albumens were used up to 1895 or 1896, but the albumen paper was produced for many more years. Developed paper was mounted on cardboard. The final image, at last, appeared in the right position, not more reversed, and with a very good definition. In 1888 one only factory in Dresden, Germany, consumed more than 6 millions of eggs for its production. A huge part of our ancestors' history is printed in albumens. With this type of pictures appeared the fashion of the "cartes de visite", personal cards with pictures. Originally the images had a cinnamon color, which becomes yellowish later. The emulsion tends to be fragile and rusty.
DRY GEL PAPER WITH CHEMICAL DEVELOPMENT
With the slogan "you press the button, we do the rest", in 1884 George Eastman, from New York, invented the paper of chemical development, which consisted in a paper treated with a dry gel of silver chloride, gel-silver bromide or gel silver-chloride-bromide. Formerly, photographers needed to transport the plates with all the chemical products and development was made by exposure to sunlight. With the new small negatives, the sensitivity of that paper produced a quick development under the electric light, allowing to make enlargements. This process was at the top of the market near 1905. These are the black and white pictures we always knew. Very soon the Kodak-Eastman also launched to the market the photographic roll.
Good conditions of photos preservation depends on not too much exposition to the light. Light creates images, but also degradates them. Photos must be touched by their edges and if it's possible, with cotton gloves. The permanence in old photos of silver salts produces rust and oxidation. By any reason metallic clips should be attached. Photos must be stored in clean rooms. If stored in albums, they should be acid free; never PVC plastics, but polyester sheets; album sheets should also be acid free papers. These kind of papers are sold by photographic stores. "Sick" pictures, with fungus or insects should be stored apart from the others; otherwise, the healthy pictures will become soon infected. To digitize an image is a good way of to preserve it, even though an original is much more valuable and it should be conserved carefully. When digitized, they must not be saved only in the computer's hard disk; it's important to save a "back-up" in a CD, DVD or a flash drive.