The first glass positives were most likely made by Nicephore Niépce using the heliograph process. These would have been both positive and negative depending on the lighting and viewing angle. In 1839 Sir John Herschel produced an image on glass sensitized with silver chloride that would have had a similar effect. The first experiments of the albumen on glass process by Whipple, the Langenheims, and Niépce de St. Victor produced direct positives on glass when the plates were underexposed and overdeveloped. The first glass positive transparencies made from negatives and strong enough to project in a magic lantern were made by the Langenheim brothers in 1849. The brothers made copy negatives of daguerreotypes using the albumen on glass processes then rephotographed them onto a second plate. They called their plates “hyalotypes.”
Two years later when Frederick Scott Archer introduced the wet collodion process he observed that underexposed negatives looked faintly positive when backed with something dark. To accentuate the effect Archer bleached the silver image to make highlights brighter and called them alabasterines. Unlike the hyalotype, which was made for projection, Archer’s positives were viewed by reflected light. Improvements to the collodion process soon made the bleaching step unnecessary. Early collodion direct positives on glass were known as daguerreotypes on glass, daguerreotypes without reflection, and verreotypes. The Cutting patent introduced a novel way of sealing the final image and also coined the word ambrotype, which became the generic term for all direct positives made on glass by the wet-collodion method. See Collodion.
The wet plate, preserved collodion plate, and a collodion emulsion process was also used to make collodion positives on glass derived from a negative. By rephotographing a negative lit from behind, the photographer could make lantern slides on clear glass or milk glass positives also known as opalotypes or opaltypes if photographed on translucent white glass. Milk glass positives and lantern slides were also made using the developed-out and printed-out albumen processes, the carbon transfer process, and developed-out and printed-out gelatin emulsions.