How Wet Gate Printing Works: Refractive Index Matching
Understand the physics of refractive index matching to eliminate film scratches temporarily during duplication or scanning.
In motion picture film preservation, physical scratches on the base or emulsion layer can severely degrade the scanned image. Wet gate printing resolves this problem through the elegant application of optical physics.
The Optical Problem of Scratches
When light passes through a dry film gate, any physical scratch on the film base or emulsion acts as a miniature lens or prism. The air-to-plastic interface bends the light rays irregularly, scattering them. In the resulting print or digital scan, this light scatter appears as dark or light vertical lines and blemishes.
Solving with Refractive Index Matching
By submerging the film in a liquid with a refractive index nearly identical to that of the film base (cellulose triacetate is approx 1.490, polyester is 1.640), the optical boundary is completely neutralized. Light traveling from the glass gate through the liquid and then into the film does not bend at the scratch's edge. The scratch becomes optically invisible.