The practice of projecting images from glass plates began centuries before the invention of photography. However, in the 1840s, Philadelphia daguerreotypists, William and Frederick Langenheim, began experimenting with The Magic Lantern as an apparatus for displaying their photographic images. Because the opaque nature of the Because the opaque nature of the daguerreotype disallowed its projection, the brothers looked for a medium that would create a transparent image.
They employed the discoveries of the French inventor, Niepce de St. Victor, who had discovered a way to adhere a light sensitive solution onto glass for the creation of a negative. By using that negative to print onto another sheet of glass rather than onto paper, the Langenheims were able to create a transparent positive image, suitable for projection. The brothers patented their invention in 1850 and called it a Hyalotype (hyalo is the Greek word for glass). The following year they received a medal at the Crystal Palace Exposition in London.
The Langenheims envisioned their slides as forms of entertainment, charging a fee to watch their picture shows. However, within a few years, lantern slides began to fulfill a variety of purposes. While entertainment remained an important function well into the twentieth century, lantern slides had the greatest impact on educational lectures, especially in visual disciplines. They played a vital role in the development of disciplines such as art and architectural history, making possible the detailed study of objects and sites from around the world.
Manufacture of Lantern SlidesThe first lantern slide producers made their slides using albumen-coated plates and, after a short period, switched to wet-collodion plates. The introduction of dry plate processes, as well as mass-produced lantern slide kits, made the slides easier for amateur photographers to produce and also made them more accessible to schools and universities.
Besides the photographic medium itself, the process for creating lantern slides remained primarily the same throughout their one hundred year history. There were two ways of printing the images: the contact method and the camera method. The first dictated placing the negative directly on the light sensitive glass. This required that the negative was the correct size to produce the 3.5x4 inch slide. For larger negatives, the camera method was necessary. Using a camera with a long bed and bellows, the negative and glass were both placed in the camera and printed by exposing the glass to daylight or artificial light. After exposure in both cases, the latent image was developed out with chemicals. After the plate was dried, the image could be hand-colored using special tints. The slide was finished with a mat and a glass cover and was taped to seal the enclosure.
The finished product was placed within a lantern slide projector to be viewed on a wall or screen. The first projectors used oil lamps for light. By 1870, limelight, produced by burning oxygen and hydrogen on a pellet of lime, offered a better, although more dangerous, form of illumination. In the 1890s, the invention of the carbon arc lamp, followed by electric light, provided a safe method for displaying the lantern slide image.