Because sepia tone softens the light in a photo, you'll get the best results with an image that's exposed well, with good contrast and a fairly full range of shades of white, gray and black. (Of course, that's the sort of image you generally want to produce, even if you're not going to alter it.)
In a conventional darkroom, sepia toning -- unlike other types of toning, such as selenium -- is a multistep process. The toner actually alters the chemical composition of the photograph, replacing the metallic silver in the image with a compound such as silver sulfide. Some people mix their own toner, but it's easier to buy a premixed commercial version [source: Frost].
First, wash the print in water for a minute or two, so the chemicals you'll apply will spread cleanly and evenly. Then, immerse it in a tray of weak bleach solution, which will fade the image and soften the highlights. Photographer and author Lee Frost recommends a concentration of no more than one part bleach to 20 parts water, which slows the process and gives you more ability to control it [source: Frost].
After bleaching, you should wash the print again for 20 to 25 minutes in cold water to remove the bleach. While it's washing, you can mix the toner solution in a tray. Most toners recommend a mixture of one part toner to nine parts water, but Frost again suggests that you make the solution even weaker. Then add the final ingredient, 10 to 15 milliliters of sodium hydrochloride, which controls the intensity of the sepia color. The more you add, the darker the tone will be. Then, soak the print in the mixture and pull it when it achieves the desired tone. Your last step is to wash the print again and dry it [source: Frost].
Sepia toning a digital photo with Photoshop or another editing program is much simpler. First, if the image isn't already black-and-white, convert it to grayscale by clicking Layer, then New Adjustment Layer, then Photo Filter. When the New Layer dialogue box comes up, set the values to Color-none, Mode-normal and Opacity-100 percent. In the Photo Filter dialogue box, enter these settings: Filter-Sepia, Density-50 percent, Preserve Luminosity-selected. You can experiment with altering the density to change the image [source: Apple].
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