About Glass Plate Negatives and Lantern Slides
Glass Plate Negatives: A Brief History
Glass plate negatives comprise two formats: collodion wet plate negatives and gelatin dry plate negatives. Both types have a light sensitive emulsion with a binder thinly layered on one side of a glass plate.
Frederick Scott Archer, a British inventor and photographer, made the first collodion wet plate negative in 1851. In order to prepare a negative, a photographer coated a clean sheet of glass with collodion, a liquid with ingredients that included cellulose nitrate and ether. Then the plate was quickly put into a silver nitrate bath in order to sensitize it to light and placed in the camera, where the negative was exposed. The photographer had to develop it very quickly after exposure. Because it was necessary to prepare, expose and develop a negative while it was still wet, this process of making photographs was complicated, inconvenient, and not very portable.
Richard Leach Maddox, a British physician and photographer, produced the first practical dry glass plate negative in 1871. In his much more convenient process, the glass plate was coated with gelatin and sensitized with silver salts. The negative did not need to be developed immediately after exposure. Maddox's method was so well-received that dry plates replaced wet. Within ten years they were produced in factories and became widely available, especially for amateur photographers. One no longer had to be skilled in mixing potentially dangerous chemicals and could store undeveloped images for long periods of time. Gelatin dry plate negatives were widely used into the 1920s. By then gelatin sliver paper negatives and celluloid roll film had become popular.
Lantern Slides: A Brief History
A lantern slide is a glass transparency that is viewed through a slide projector that casts the image on a wall or other surface. Centuries before the invention of photography, painted images on glass were projected for entertainment. In the 1840s, William and Frederick Langenheim, daguerreotypists in Philadelphia, first used a glass plate negative to print onto another sheet of glass, thus creating a transparent positive image that could be projected. Well into the 20th century, lantern slide projectors displayed photographic images for entertainment as well as education. Lantern slides were not difficult to produce in mass quantities and were therefore easily made available commercially.
Usually a lantern slide was created by placing a dry plate negative directly on light-sensitive glass, which, after it dried, was fitted with a cover glass and mat and sealed with tape. Sometimes a slide was hand-colored with special inks before it was covered. The lantern slide could be viewed through a projector with a light source that changed over time--oil lamp, limelight, carbon arc lamp, and then electric light.
Handle with Care
Glass plate negatives and lantern slides are very fragile and require careful handling, since they easily chip, crack or even break. The emulsion on the glass is vulnerable to scratching and flaking. The glass plate negatives in the Archives are stored vertically to help prevent pressure being placed on them. As resources and time allow, they are being scanned and then rehoused in acid-free enclosures and boxes.