Lantern Slides
Lantern slides, also known as magic lantern slides, were first produced in the 1650s and used by educators, lecturers and entertainment providers. Images were hand–painted onto glass slides which were illuminated and projected with a magic lantern using a convex lens. Presenters often added elements to the slides in order to make them appear to have movement, adding to the entertainment and educational value. Using the pre-electricity lanterns proved to be hazardous, however, as they were fueled by burning candles, kerosene or gas.

Hand tinted (colour) lantern slide collected and used by Tex Vernon-Wood, hunting guide and outfitter in the Canadian Rockies. Hoodoos in the foreground. Glenbow Library and Archives, UCalgary: S-233-90.

Tea house in the Canadian Rockies, [Alberta or British Columbia]. 1920s or earlier, possibly Lake Agnes Tea House in Banff National Park, Alberta. Lantern slide, black & white, hand tinted. Digital Identifier: S-28-39
History of format
Philadelphia brothers William and Frederick Langenheim introduced photographic lantern slides in the mid-1800s, a few years after the invention of photography by Joseph Nicéphore Niépce in France.
Process
Using a 3.25–inch light-sensitive glass square and the wet collodion or the dry gelatine process, negatives were exposed under light. The resulting positive black and white images were often hand-coloured using transparent oils and watercolours. Once the image was set, a second glass slide was placed on top of the image and the two pieces were taped together.
How the format was used
Lantern slide manufacturers quickly began producing boxed sets of themed images to be used by teachers, travellers, clubs, and anyone else that wanted to organize presentations to various audiences. The invention of electricity in the late 1800s made projecting the lantern slides with light bulbs much easier and safer. As new photographic films started to emerge in the early to mid-1900s, first by Agfa and then Kodak, lantern slides were eventually phased out, giving way to 35mm colour slides.

Shipment of gold leaving Dawson City, Yukon. 1898-1900. Photographer: Hegg, E.A., Dawson City, Yukon. Slide annotated: "1 & 1/4 million dollars." From the black and white image in E.A. Hegg's Souvenir of Alaska and Yukon Territory (published 1900), page 74. Lantern slide, black & white, hand tinted. Glenbow Library and Archives, UCalgary: S-227-136.
Learn more links
The Magic Lantern Society of the US and Canada
The Henry Ford – The History of the Magic Lantern
Royal Geographic Society – Researching the collections: Lantern Slides