Censoring of silent films required removing scenes with offensive imagery, and removing or replacing title cards. This was easy to do, by physically cutting out the offending strip of film, and splicing the sections before and after the cut. When done well, a viewer would never even know a cut had been made. In some cases the censor office would make the cut, and advise the distributor, but in other cases the censor would request the cut, the distributor would make it, and sometimes send the censor office the offending section of film as proof that it had been removed. While cutting did require some work, keep in mind that there was often only one copy of a film circulating in a province. As late as the 1950s, censors would note if cuts had been made to a second or, rarely, third print. Although silent films often showed people talking, censors did not lip read films, and occasionally a film with mouthed profanities did slip through, such as What Price Glory (1926).
The arrival of sound in the 1920s meant everything spoken was recorded, including double entendres and other objectionable dialogue. Cutting audible dialogue posed problems. The first commercially viable movie sound system was sound-on-disc, basically a large (16″) record that was played along with the film, one record per reel. A reel of film was about eleven minutes, and the technology of the time required the large record to store eleven minutes of sound. Not all censor offices could play the record, and even if they could, and did hear something objectionable, it could not be cut.
Vitagraph, the developer of sound-on-disc, tried to prevent the need to censor sound by claiming sound was not really part of a film, and therefore not subject to the film censorship requirements. The issue came to court in Pennsylvania, location of one of the more aggressive state censors, and the state supreme court ruled against Vitagraph. (Vitagraph was bought by Warner Brothers in 1925, which christened the sound-on-disc process VitaPhone. The term was later used for any sound film, and into the 1960s was used for shorts.)
Fox (which merged with Twentieth Century in 1935) also opposed censorship of sound, and also lost in court. In their case, Fox refused to submit written copies of the dialogue, an aid to censors. The Pennsylvania Supreme Court ruled that printed dialogue submission was required.
The film companies accepted that sound in films was subject to censorship, and supplied printed scripts to censors. Dialogue cuts were handled by instructing the projectionist to turn down the volume when necessary. For example, the 1931 comedy short Hello Russia includes the 1917 song “You’re in the Army Now” (one of many film appearances of this song). A line in the song starts “You’ll never get rich” and ends with either “you son of a bitch” or “digging a ditch.” It’s not clear which version was in the film, but according to archival records in British Columbia, the line had to go in order for the film to play in that province.* The local office of Canadian Universal replied to the censor’s request, confirming the arrangement:
Please be advised that owing to censor cut of dialogue in the two reel talking comedy, entitled HELLO RUSSIA, as follows,
“You’ll Never Get Rich – ”
whenever this subject plays a disc account a letter will accompany same, instructing the operator to pull the fader and thereby eliminate this dialogue.
Projectionists could lose their license for failure to observe censorship instructions.
In the early 1930s there was format war over film sound, and the less cumbersome sound-on-film system won. Sound-on-film is an optical process. A light shines through a small section at the edge of the film (the soundtrack), where there is a line that varies in thickness and shape. A sensor registers the light variations and they are converted to sound. With sound on film, cutting the film to remove an image would also remove the sound. However, sometimes only the dialogue needed to be removed. This could be done by obscuring the soundtrack. Censor records sometimes mention that dialogue was “zaponed.” It’s unclear exactly what this meant, but it probably refers to applying a coating to obscure the optical soundtrack. Zapon used to be a brand name for a cellulose nitrate varnish, a coating similar to nitrate film stock.
Analog optical soundtracks are still used for films, but usually supplemented by one or more digital optical soundtracks, resembling tiny barcodes. Sound on disc also made a comeback of sorts, in the form of a proprietary system that used CDs for film audio, synchronized with the film by (digital optical) codes on the film.
Actual film has become rare. Halifax has 45 commercial theatre screens, and only one can show films. Most movies are distributed to theatres as digital files, which are much larger than the files used for home viewing. Digital files make censoring easier, and have the potential to make it as invisible as it was in silent films. At home, ClearPlay allows viewers to stream or view their own discs, with dialogue and scene censoring on the fly, according to their own personal preferences. However, this has not happened (so far) with theatrical releases. Classification agencies no longer review scripts or demand dialogue cuts, and anything potentially objectionable is simply taken into account when assigning the rating.
A legacy of sound-on-disc is the frame rate of films. Silent films were projected at various speeds, usually between 20 and 26 frames per second. The projector operator might run the film faster or slower to enhance the comedy or drama of scenes. However, the need to synchronize the film and the record, and the greater sensitivity of the ear to variation in sound frequency than variation in image frequency, meant that sound films had to run at a constant fixed rate. Vitaphone set this at 24 frames per second. This is still the standard for film projection, and most digital projection, though higher frame rates are becoming more common.
*British Columbia was not necessarily stricter than other provinces, but they appear to be the only province that kept records of censorship requests.