|WWI Propaganda slide manufactured using isinglass transparency|
Some of the slides were constructed using prevailing double-pane class design, but others were created by either stencil-cutting text into metal sheets or by printing directly on to a transparent material which I mistakenly identified as cellophane.
After having a look at the article (which incidentally featured slides from their collection) my friends at the Niles Essanay Silent Film Museum suggested that it was isinglass, not cellophane, which was used as the transparent material in the cheap government slides.
Isinglass? What the heck is that?
|Modern isinglass product|
As it turns out, there are two different substances that go by the name isinglass. The first is a form of collagen created from dried fish bladders which today is used primarily for clarifying wine and beer. Yes my Irish friends, the Guinness you're drinking may contain traces of fish bladder.
|My $6.69 isinglass sample|
In the "olden days" isinglass (mica) was used in place of glass in certain circumstances. For example, Model T cars were equipped with canvas curtains featuring isinglass peep holes. Even today isinglass is often used instead of glass to cover peep holes in boilers and wood burning stoves because it less likely to shatter when exposed to extreme temperatures.
As part of my in-depth scientific inquiry, I recently purchased an isinglass stove window ($6.69 on eBay) to test and compare to the WWI slides in the Niles collection. Eureka! It's the same stuff. It is lightweight with a color that is just slightly yellowish, and it behaves very much like plastic. I was able to easily staple through my sample with a standard office stapler, cut it with scissors, and write on it with a ball point pen. The only thing different about it is that it won't burn - a very useful property for a material that would have been subjected to the heat of carbon arc projection lanterns.
"...The wheels are yeller, the upholstery's brown
The dashboard's genuine leather
With isinglass curtains y' can roll right down
In case there's a change in the weather
Two bright sidelight's winkin' and blinkin'
Ain't no finer rig I'm a-thinkin'..."
-- The Surrey With The Fringe On Top from the Rodgers And Hammerstein musical OKLAHOMA!