standpipe to hold water in the sink at the correct depth,yet still allow water to flow out (fig. 10-1).SAFELIGHTSThe function of a safelight is to transmit themaximum amount of light that can be used safelywithout damaging the sensitized materials beingprocessed. The color sensitivity of different sensitizedmaterials varies. Therefore, the color and intensity oftransmitted light must be varied accordingly. Adarkroom safelight is the combination of a rated lightsource and a filter designated to protect a specificsensitized material.The word safe. of course, is a relative term since nosensitized photographic materials are ever completelysafe from the effects of safelight illumination. However,a filtered light is accepted as safe when the sensitizedmaterials can be handled under the illumination with noevidence of fogging for at least twice as long as thenormal processing time. No procedures must befollowed precisely when safelights are used:303.23Figure 10-1.–Photographic processing sinkUse only the size of incandescent bulb specified;for example, 7 1/2 watt, 15 watt, or 25 watt.Handle sensitized material at the distancerecommended by the manufacturer. This is usuallybetween 3 and 6 feet.To determine whether a safelight is safe, you shouldfollow these procedures:1. In the dark, place a sheet of unexposed film,emulsion-side up, on the working area where the film isto be processed.2. Place several coins on the emulsion and turn onthe safelight. Leave the safelight on for twice the lengthof time the film will normally be processed.3. Process the film normally and check to seewhether there is less density in the areas covered by thecoins. When there is less density, it indicates the filmwas fogged by the safelight and the safelight is not safe.A safelight that causes fogging may be corrected byreplacing the filter, by installing a lower rated bulb, or10-10
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