At Luna, many of us have backgrounds in what is now termed “analog photography.” That history comes in really handy when we are asked to digitize collections containing a variety of ancient film types, taking into account their peculiar handling characteristics and imaging properties. As examples, it’s amazing how many obscure and now mostly forgotten 35mm film types were used for slide-making (yes, that was an occupation) in the dim past. However, these films still show up in slide collections to be digitized, so I think it’s worthwhile running down a list of some of them. I can remember ten of them, none of which are available today!
Color Positive Films – Ektachrome 64 Tungsten, also called “EPY”, was very commonly used for slides of color originals shot on a copy stand. It produced beautiful images. Then there was Ektachrome 100 Plus, also called “EPP.” It was a daylight-balanced film that was used in film recorders (remember those?) to shoot presentation slides mostly from Powerpoint files. The typical university department would have a departmental film recorder, which they more often called a “slide-maker”, and faculty would have to fight each other for access to it. Finally, there was Ektachrome Slide Duplication Film, 5071, used for what its name indicates.
High Contrast B&W Negative Film – Kodalith Ortho film was used to make slides from black type or graphics on a white background. The resulting image on film was reversed with a totally opaque background and clear lettering or graphics. When projected, the image appeared to float onscreen with no frame. Because the background was opaque, the film could be painted with Dr. Martin’s transparent watercolors, creating colored images floating on the projection screen. Another popular technique was to contact print the Kodalith negatives onto diazo sheet film using ultraviolet light. After exposure, immersing it in extremely noxious ammonia vapors would develop the diazo film, which came in a variety of colors, blue being the most popular. The sheets would then be cut into individual frames to be mounted. Diazo slides are a challenge to digitize, since they are usually badly faded.
High Contrast B&W Positive Film – Kodak’s Precision Line Film, LPD4 was used to copy originals similar to those used with Kodalith, but producing a direct positive image with black lines on a clear background. There actually is a technique for producing the same result by reversal processing of Kodalith! It uses hydrogen peroxide as the bleach. If you are interested in arcane photographic processes such as this, send me a note, and I’ll send you the procedure.
Continuous Tone B&W Positive Film – For copy slides of B&W pictorial originals, one could use color film, but an easy and inexpensive alternative was Kodak’s Rapid Processing Copy Film, also called RPC. Originally developed for copying wide tonal range X-rays onto 35mm film, it was indeed rapid processing, but it was anything but rapid exposing. Whereas modern digital cameras might have a minimum sensitivity of ISO 100, and Kodalith’s sensitivity was about ISO 6, RPC’s sensitivity was the equivalent of about ISO 0.06! So the exposure time for each frame was typically in the neighborhood of 45 seconds. There was a payoff, however. RPC’s film base had a slight blue tint, which made projected images look very clean, since projection bulbs tend to emit light on the yellow side.
Instant Slide Films – Finally, there were three Polaroid instant 35mm slide films that should be mentioned. Polachrome was for color originals, Polapan was for continuous tone B&W originals, and Polagraph was for high contrast B&W originals.
It’s interesting how teaching slide collections can encode not only the subject matter of what was taught, along with how it was taught, but also a pretty fine-grained view (pun intended) of the imaging technology used to teach it!