Remove Before Projecting
July 28, 2010
Last Thursday I described the two primary manufacturing designs for coming attraction slides. The original design used two identically sized glass panes (a glass sandwich) in which the image-carrying glass pane by covered by a second clear glass pane which protected the vulnerable photographic emulsion. An alternative slide design was introduced in 1924 which utilized only the image-carrying glass pane embedded within a surrounding cardboard frame.
The cardboard frame design was patented (Patent #1,500,025) by Alvin L. Mayer of Long Island, New York, and boasted the advantages of lower weight and reduced manufacturing cost. One disadvantage of Mayer's design was that by eliminating the protective pane of clear glass, the slide's image-carrying emulsion was exposed to scratches, dirt, and damage.
Of course, for a product originally designed to be discarded after use, this was probably not considered to be much of a downside.
In his design, Mayer addressed the issue by including a removable cardboard shield which covered the glass during transport: "In order that the emulsion or film side of the plate may be further protected during transportation, the opening in one of the end sections may be temporarily closed by a shield which is easily detached before the plate is exposed."
Until the other day I had never seen an example of a slide with the cardboard shield still attached. Fortunately, a friend/collector shared with me a slide of of Mary Pickford's Cocquette (1929) manufactured by Combined Photo Industries, Inc., which still included the the protective shield. Now I know it's hard to get too excited about a 2 7/8" by 2 3/8" cardboard square, but having never actually a slide with the shield in place I thought it was pretty cool.
Finally, as a post script for the technically minded of you, here's the diagram from the original patent application. I have used yellow to highlight references to the protective shield (labeled A2 in the diagram).