Film Preservation 101: Scratch Hazards and Fixes

For those working with archival films, encountering film scratches is just part of the job.

At the National Archives we care for films that range from pristine camera negatives with not a scratch to be seen, all the way to beat-up projection prints that look like they were rubbed with sandpaper. Scratches can be black or white, depending on whether they are on the base (the plastic carrier) or emulsion side of the film, and whether the film is an original or copy. Color film sometimes contains colored scratches.

Most often a film is scratched when it is handled or projected. A dirty projector gate can permanently gouge a film during a single playback.

And then there’s this:

This still from item 342-USAF-42644 has a prominent emulsion scratch caused by the camera used to shoot the film. You can see a pile of emulsion shavings in the upper left corner of the screen.

We can tell that this scratch is in the emulsion because the blue tone to the scratch indicates that other colored layers of emulsion, made up of silver halide and gelatin, have been scraped away. The astonishing thing about this image is that the blotch in the upper left corner is made up of shavings of the missing emulsion. The scratch is coming from inside the camera!

In the above clip, presented at 10x speed, you can watch the pile of shavings build up as the film runs through the camera. The photographer either did not clean the camera gate or loaded the film incorrectly so the film’s emulsion side scraped against a spot sharp enough to scratch. We don’t often see films in the National Archives that were scratched at the point of capture like this, but it clearly demonstrates the hazards of an inattentive camera operator.

Once a film is scratched the flaw cannot easily be removed from the surface. Standard copies made from the film will contain a line in the image, carried over from the physical scratch. There are some techniques to minimize the appearance of scratches in new copies made from the film. Scratches on the base side of film can be wet printed, using fluid with optical properties similar to film base to temporarily fill in a scratch. If the emulsion where the image resides is scratched off, the only remedy is digital restoration, which can effectively mask scratches but only approximates the information contained on the missing emulsion.

In the National Archives Motion Picture Preservation Lab, we do everything we can to prevent scratches, including keeping equipment clean and in good working order, handling film carefully, and double-checking our film threading. We use available tools to address scratches that have accumulated over time in our preservation and restoration work. However, in the case of a camera scratch, that’s just part of the film record.

The edited film clip in this blog post comes from Reel 1 of Crew Chief/ Door Gunner (UH-1Ds), Vietnam (342-USAF-42644). The whole reel may be viewed on our YouTube channel. The camera emulsion scratch begins at 11:23.

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