Silver sulfide soundtracks on 16mm color reversal prints(1938–1972)

When 16mm Kodachrome film was introduced in 1935, it was initially intended for direct projection of the camera original. If a copy was made directly onto Kodachrome camera stock, the copy would tend to display excessive contrast. For this reason, special reversal duplicating stocks were produced to avoid contrast build-up. Later on, “commercial” camera stocks were introduced to provide better results when duplicating.  

Printing an optical soundtrack on B/W film was relatively straightforward, as the processing of the soundtrack could be done simultaneously with the picture. When multilayer color reversal films (specifically Kodachrome) became available, certain issues were immediately evident.  

The yellow and magenta emulsion layers could not be used for soundtracks, as they were essentially transparent at the wavelengths to which the photocells used in sound playback heads were most sensitive. The cyan layer was potentially usable but was unsatisfactory as it was the deepest layer, and the outer layers would disperse the light, thus reducing the resolution of the cyan image (Mannes & Godowsky, 1939). A dye track also has an inferior signal-to-noise ratio compared to a silver track (Dearing, 1941). It was also possible to produce a dye track using all three emulsion layers, but that was also found to produce inferior results (a reduced high-frequency range) (Mannes & Godowsky, 1939; Dearing, 1941). Therefore, it was deemed preferable to produce the optical soundtrack in the top (yellow) emulsion layer only – but it had to be opaque to red wavelength light. The silver sulfide soundtrack offered a practical solution to these problems.

(The term “silver sulfite” soundtrack is used in multiple sources – while incorrect, its use is widespread.  From the patents, it is clearly “silver sulfide”.)

Kodachrome Duplicating Film 5262 was introduced in 1938, two years after the introduction of 16mm Kodachrome camera film. This new duplicating film was well suited for printing silver sulfide soundtracks. It could also be used as a camera stock when reduced contrast was desired. Before this time, one can assume that duplicates were made on Kodachrome camera stock, resulting in excessive contrast. 5262 was replaced with Kodachrome Duplicating Film 5265 in 1940, which was used until 1956 when Eastman Reversal Color Print Film 5269 was introduced. Print film 5269 was also based on Kodachrome technology, but was intended for producing silver soundtracks, rather than sulfide tracks. So, 1956 marks the end of sulfide tracks on Kodachrome release prints. (Eastman Kodak, 2017)

Ektachrome reversal print film 7386 used a silver sulfide track produced in the same manner as Kodachrome Duplicating Stock 5265. Reversal stock 7386 was introduced in 1960. By this time, Kodachrome type print stocks were already using silver soundtracks, but this was still not possible with Ektachrome stocks. Later Ektachrome reversal color print stocks, such as 7389 and 7390, introduced in 1970 and 1973, were suitable for silver tracks (Eastman Kodak, 2017) (Tremaine, 1969: 18.286 & 18.287). These developments signaled the end for the use of sulfide soundtracks.

Silver sulfide tracks were also used on Anscochrome and Gevachrome print stocks (Verbrugghe, 1967).  

There are few well-known film titles printed on 16mm Kodachrome, or Ektachrome Duplicating stock – these stocks were used mostly for educational and industrial films, with the occasional use on TV shows. Sometimes 35mm Technicolor films were printed on Kodachrome Duplicating stock for 16mm release. Until the Eastman Color negative–positive process was introduced in 1953, all 16mm release prints were made on a reversal stock, such as Kodachrome or Agfachrome, or using a multi-strip process such as Technicolor, or Cinecolor. Technicolor and Cinecolor were only cost-effective for large print-runs, and could not be produced as quickly as reversal prints. Later, as most 16mm production continued to be on reversal camera stocks, short print-runs could still be made more quickly and economically on reversal stock, as it negated the need for the production of an internegative.