Why do most Civil War photos look a little brown? Why when we see photos with brownish tones do we assume they were taken long ago? Both of these questions stem from the same concept: How sepia toning became the preferred way to stabilize photos and to make them "warmer" to the human eye than the standard grayscale images produced in the early days of photography.
When silver nitrate first was used to produce positive prints, or photographs, the black-and-white images were starker and harsher than the colors we see. They also appeared to be "cold" because of the lack of color. Photographers also discovered the photos could fade and disappear if nothing was done to stabilize them. So, in the mid-to-late 1800s, photographers began toning their photos and adding sepia, a brownish red pigment made from cuttlefish, particularly those found in the English Channel, to photographs.
Sepia pigment essentially replaces the silver in prints, thus turning them brown. Since this it is a sulphide, it doesn't fade as quickly or as easily as silver. Matthew Brady, the famous Civil War photographer, sepia toned many of his iconic war images. While his work went out of vogue rapidly after the Civil War and bankrupted him, many of his images have lived on because they underwent sepia toning.
Other than classic black-and-white photographers, such as Ansel Adams, who used the stark blacks and whites effectively, photographers use toning to change the mood of their photographs. They use reds in various degrees, for example, to make their photos appear as if they're being seen through rose-colored glasses; they use blues to give their photos colder tones, which is especially useful for winter scenes. Sepia adjustments have always been a popular standard, particularly to give an old-fashioned effect.
Any black-and-white image can be toned, whether it's a print or a digital image. The way to sepia tone a print is to fully develop it, rinse it, fix it and wash it. Then, you bleach the print thoroughly. To get all the bleach out, wash the print again in water. You can leave it in the bath longer for a darker brown look; less time will give it a faded look. The print is then washed again. To do the same thing on a digital image in Adobe Photoshop, you can do one of three things. Open the photo on your computer. If it is a color image, go to Image>Adjustments>Desaturate. This will keep a wide variety of grayscale tones. Then go to Actions>Sepia Toning (Layer). This will create a new adjustment layer with a preset sepia effect. The second way is to turn the color image to grayscale (Image>Mode>Grayscale) and use Actions>Sepia Toning (Grayscale). Both of these will give a reddish brown sepia tint. The third way is to go to Image>Adjustments>Desaturate, then go to Image>Adjustments>Variations. This gives you a little more control over the tone by adding red, yellow and other colors and making a custom browner tint.
With the demise of film---although there are some who still use it---digital photography has tried to replace everything once available in traditional photography, including sepia toning, but without the unpleasant chemicals. Some digital cameras have a sepia tone filter built in so you can shoot with it automatically. The safer way, however, is to shoot traditionally and then use the sepia tone setting in Adobe Photoshop. Although, for some uses, this process makes a color image a little too red.