the film in the transparent substrate that forms the film base, rather than in the photographic emulsion on the front that holds the film's actual image. In the normal process of duplicating a film in an optical printer, collimated light passes through the film base on its way to illuminate the emulsion. Any scratches, abrasions, etc., in the film base cause the light to bend such that the duplicated film ends up with bright or dark (depending on whether copying from a negative or positive original) copies of the scratches. This bending of the light is being caused by the difference in the refraction index of the substrate and the air. If these scratches and abrasions can be prevented from being captured on the new print, it eliminates one entire area of restoration work. Three methods address this problem. First, one can simply enlarge the portion of the film not damaged. This mainly has application where the damage is confined to the edges. The second method is wet-gate printing. The "gate" in a projector is the apparatus that holds the film in place as each frame is shown. A wet gate is filled with a fluid that coats the film as it is fed through, constantly replenishing the fluid as needed. Wet gate printing eliminates the refraction itself by filling in the gouges in the substrate with a fluid such as perchloroethene that shares approximately the same refractive index as the substrate. With the fluid temporarily displacing the air in the scratches and abrasions, refraction simply no longer occurs, so the defects are not reflected on the new copy. The light used is fully collimated, as with standard optical printing, and the film is undamaged by the process. This method does not work if the scratches on the emulsion side are deep enough to have removed some of the silver or dye image in the original film. The third method involves inserting a diffusion filter in the path from the collimated light source to the film. It can eliminate the projection of small defects on the back side of the film onto the new copy because the light, rather than arriving at the back of the film in perfect parallel lines, instead enters the scratch from several directions. It is therefore still diffuse when it exits, ensuring an image of the scratch will not show up as strongly on the