The earliest method for producing color photographs was to hand-paint the print. Here is my first attempt with water colors.
Another method to introduce color involves chemical toning of a print. The basic idea is that the silver grains are replaced by another element, such as iron, nickel or selenium.
The most widely seen toning is called "sepia", producing a beautiful brownish tint. Iron toning makes the image blue, while nickel toning is pinkish or magenta.
To do iron toning, you should start with a "weak" print, that isn't too dark, as the toning process darkens it - which can also be advantageous to improve a weak print. Selective toning involves masking out the regions you don't want to affect with a liquid rubber (latex) solution called art masking fluid, and allowing it to dry.
Iron toning is among the simplest processes, since it is a single-step toning. Of course, chemical safety must be observed! (I take no responsibility for your results or lack thereof, or any issues related to the chemicals.) The Darkroom Handbook has the following recipe:
Solution A
Solution B
Mix equal parts of A and B solutions before use. Pre-soak the print and place in the toner solution face up. Remove and rinse for 10 minutes when the desired coloration has been achieved.
As you can see, the results will depend on the original print (brightness and contrast), as well as the length of time in the toner - Marilyn was toned for a shorter amount of time than the glass sculpture. The rose was a lighter print than the wellhouse roof. Of course, after scanning, digital manipulation of brightness, contrast and hue are easily done.
Careful inspection of Blue Marilyn shows my inexpert application of the rubber protective layer, with some cracks allowing toning in undesireable areas and generally poor contouring around her face. Practice makes perfect!
Nickel toning produces pink/magenta prints, starting with a slightly contrasty black and white print, as it reduces contrast a bit. It requires three baths, plus rinsing, so is a bit more complicated than iron toning.
Bleacher Solution A
Bleacher Solution B
When ready to use, mix equal parts A and B solutions, acidified with a few drops of citric acid.
Toner Solution
You will also need 5% Hypo fixer solution, such as Kodak fixer (25 g in 500 mL water, for example).
Wearing rubber gloves, mix the bleacher A/B and citric acid. Bleach the print until no trace of the black silver image remains (for full toning - partial toning is possible, also.)
Fix for 5-6 minutes in the hypo fixer and then rinse thoroughly. Place the bleached print in the toner and watch the pink image emerge (it takes a couple minutes to begin) until the density is as desired. Wash the print for 10 minutes to complete the process.
The toned statue above actually started from a very dark contrasty print on warmtone paper, while the black and white version is a more normal looking print, on cooltone variable contrast paper.
Sepia is the most well-known of the toners, producing a beautiful brownish hue. Various recipes are used, with the following being one possibility.
Bleacher
Dilute bleacher 1:9 for use.
Toner (re-usable)
The thiourea solution gives off less odor, and is what I have used here.
Bleach for 2-3 minutes and rinse for 1 minute. Then place in the toner for 1-2 minutes, until the desired tone is achieved and wash thoroughly.
The final results will depend on the initial print density and contrast, as well as the bleaching and toning times.
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