The earliest existing photographs were direct exposures on sensitized silver coated metal plates (daguerreotypes) and some sensitized paper. Such pictures were unique and could not be duplicated. Once photography began using glass plates, it became possible to use the glass negative as a means of making copies to coated, sensitized paper. Early glass plates needed to be sensitized to light, just before they were exposed. These were generally called “wet plates”. This “collodion” process used flammable nitro-cellulose (gun cotton) as the emulsion which contained the light sensitive chemicals and held them on the plate. The plate was made sensitive by soaking in a liquid bath. The picture needed to be taken quickly before the plate dried. These difficult procedures largely made picture-taking the realm of professionals. By the 1880s, commercial “dry plates” made photography much more easy and affordable. The camera was now able to become available to non-professionals and pictures began to be taken in many more subjects and contexts than ever before.
These plates would be unwrapped in a dark room and loaded in protective magazines. A magazine would be loaded into a camera and a slide would be pulled out to prepare for exposure. A picture was taken and the protective slide was replaced. Two plates were contained in a magazine. Once a picture was taken, the magazine could be flipped around and the opposite side could be used. This camera outfit pictured included four magazines for a possible eight exposures.
This type of glass negative has a gelatin based emulsion and survives very well, as long as they are not exposed to moisture or condensing conditions. Of course, scratching and breaking them doesn’t help!
Glass negatives are among the best surviving forms of vintage photography. Their care is fairly easy, but still must be respected. Avoid flat stacking, so as to create enough weight pressure to risk breaking glass. Loose grit and dirt should be removed, using a soft cosmetic brush or clean microfiber cloth. Clean plates aught to be kept either in their original envelopes, or sandwiched between new, acid-free paper. The dull, emulsion side of the plate is where the image is kept, and is soft and porous. It is easily scratched or damaged by moisture and fingerprints. The opposite, bare glass side may be more aggressively cleaned as long as the emulsion side is not effected. Dry plates tolerate a wide range of storage temperature, as long as condensing conditions are avoided.
NEVER try to glue or tape back together a torn photo paper print or broken glass negative! This will cause more damage. Scanning and computer edited restoration may be able to completely reconstruct the image! Store the pieces in cotton or soft cloth so the gelatin coating is not allowed to flake away.
Water and even moisture may stain the emulsion, which cannot be removed. The gelatin layer may also want to flake away from it’s glass base. It is possible to clean the shiny, bare glass back side of the negative, but the gelatin side may only permit a light cleaning with a soft cosmetic brush or clean microfiber cloth.
AVOID MAKING FINGERPRINTS! Fingerprints are food for mildew. Although these can be cleaned off of surfaces, like glass, they usually cannot be removed from porous surfaces. Mildew will grow rapidly when your storage area experiences high humidity. Mildew will penetrate and damage many vintage media materials, such as movie films, glass and film negatives, and wax phonograph cylinders.