Overview

In camera and film technology, a "scratch" refers to a mechanical damage to the film surface, which appears in the image as a continuous, usually vertical (in the direction of film travel) line. Scratches are a classic film defect phenomenon of analog production: they occur when the film material runs along a solid particle or edge during transport, damaging the base layer or the emulsion layer.

Related, but not synonymous, is the English term "hair in the gate": this refers to a lint or splice that protrudes into the image gate and becomes visible there as a mostly static dark shape at the edge of the frame – not a longitudinal scratch caused by abrasion. Both problems occur in the image gate and are intercepted by the same control ("Check the Gate"), but they are different defects. A permanent scratch on the negative is transferred to every print and is practically irreversible in analog.

Causes and Appearance

• Location of origin: typically in the image gate, at the pressure plate, or generally in the camera's film path; also possible in the projector and scanner.
• Trigger: dirt, dust, abraded material particles ("splices"), or crystal deposits that lodge between the film and the mechanism.
• Direction: Longitudinal scratches run in the direction of film transport; transverse scratches tend to indicate errors during loading.
• Position: Scratches can be on the base side or the emulsion side. Base-side scratches are easier to mask; emulsion-side scratches mean actual image loss, as image information is missing.
• Visibility: On the negative, scratches can appear as clearly visible lines in the later positive print – base-side scratches tend to print as light/white, emulsion-side scratches as dark/black. In color negative, depending on the affected color layer, colored (e.g., yellowish) lines can also occur.

Use on Set and in Post

To prevent scratches, the image gate is checked after critical takes: on the call "Check the Gate," the 1st AC (focus puller) checks the gate for lint and particles before moving to the next setup. Cleaning is done carefully, for example, with orangewood sticks or compressed air. Clean, regularly maintained equipment is the most important preventive measure.

In restoration and film scanning, scratches can be partially reduced: during wet-gate scanning, the film is passed through a liquid with a similar refractive index, so that shallow base scratches are optically "filled in"; digitally, lines are removed using Dust & Scratch Removal software.

Distinction

Not to be confused with the homonymous audio term "scratch track" (temporary reference/guide track) or "scratch disk" (temporary cache memory in video editing). In camera/technology, "scratch" refers to the physical scratch on the material. Also to be distinguished from the related "hair in the gate" (lint/splice protruding into the image gate), which is not a scratch.