It used to be essential for post-production, and we bet you’ve never heard of it!


Replay: Rubber Numbering, these words will evoke either a pinch, maybe a tear, nostalgia or a baffled shrug. It may look like a relic from British colonial times, but it was neither made of rubber nor intended to enumerate it. It was, however, once an essential part of film post-production..

“Rubber numbering” was the colloquial British term for edge numbering or edge coding machines (“rubber” referred to a latex-based solution used by early machines). There was a constant demand (all film editors needed it) and a limited supply (these were specialized machines produced in small quantities), so that it could become a “good little income” for those who. had one. But to explain what he actually did and why it was essential, we have to look back at how film editing technology worked in the pre-digital age.

Audio for films in the second half of the 20th century was typically recorded on “tape” and then transferred to punched magnetic film. Urgent (or daily) prints of the film, in 16mm or 35mm, had to be synchronized. with the audio track, usually by lining up the slate click.The wizard would synchronize the picture and the sound, inserting a blank spacer if necessary, ending up with an image roll and a sound roll, perfectly in sync. The problem then was that once you started cutting the image and sound, you would most likely lose sync unless you meticulously marked each cut, on both sides and both rolls, with a unique number. The alternative was to put matching numbers into your newly synced rolls so that each cut image could be matched with its corresponding audio. And that’s where the rubber numbering machine comes in. houc.


The machine was a simple mechanical device that took the synchronized rollers and marked the corresponding numbers on the edge of the image and sound as they were routed, using a hot foil stamping process. or adhesive tapes, effectively putting physical time code on both rolls. These numbers are not to be confused with any edge numbers or KeyCode numbers made in the negative that were used to match the original negative to the cut print (the cut copy) in the final step of the printing process. editing. here is a short film which shows the process.

The main manufacturers in the UK were Acmade (the inventors of the Pic-Sync) and Moy (famous for their gear heads), but there were also a few smaller competitors. Many editing outfits benefited greatly from the revenue from a machine that sank into a back room. If a TV company came back from a shoot with a lot of material that required synchronization and numbering, they would often outsource the work to whatever facility was available.

While people were still editing film, the rubber numbering machine was in demand. Although time code was used in the 1980s on both audio recorders and cameras (either exposed on the negative by the camera itself or through the use of clap [slate] which displayed the timecode), the editors still needed the physical numbers on their rolls in the cutting room. It was only when the negative was transferred directly to video that the time code took on its full meaning; the time-coded rushes would be automatically synchronized in the telecine suite.

acmade 2.jpg

Of course, today the rubber numbering machine is now confined to the trash can of history and you would be hard pressed to find one outside of a museum. His last appearance on the world stage was in 2013 when Ken Loach, possibly the last great director to actually edit on film, launched a worldwide appeal for duct tape for his numbering machine. The unlikely saviors were the Pixar productions in California that made FedEx in their last 19 rolls.

So, what are we interested in today about the rubber numbering machine? Well, it might be worth remembering how surprisingly easy editing has become since the laborious days of film editing. The idea that the time between shots was represented by physical hardware (spacer) seems positively strange today, as does the idea that image and sound could be physically hung in a trim bin might have. a certain attraction for analog enthusiasts.


Ken Loach aside, I can’t imagine anyone wanting to go back to those days, but in the digital world there really is no equivalent today of a simple but custom-built mechanical device that can not only generate much needed income for a production or post-production company, but can also provide an entry point for new entrants to the industry.

I wonder if there are any readers here whose first job in the business was to operate a rubber numbering machine in the back room?


Leave A Reply