This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Bear in mind, if a color is too strong on the print it may be reduced to a certain extent by simply rubbing with the stump. If this fails to give the desired result, apply a little turpentine to a clean stump, and after allowing it to set for a second or two, rub the surface gradually. This should sufficiently remove the superfluous color and enable one to obtain the proper reduction. Then by careful manipulation, using this same stump, the colors can be made to blend, unless the stump is too heavily charged with the turpentine. In such a case apply a tuft of dry cotton.
Final Cautions. - When heavy, coarse platinum papers are used the surface must be gelatinized with a double coating. Smooth platinum paper usually requires but one gelatin coating. Unless dried in a room of 80° Fahr. the gelatin coated print should be allowed to stand for two hours before applying the oil colors. Gelatin, collodion and carbon prints need no gelatin sizing, as the emulsion keeps the turpentine from penetrating into the paper.
In preparing the turpentine for platinum papers, poppy oil, or boiled linseed oil, should be added. Use a few drops of the oil to two drams of turpentine. For collodion surface papers no oil is required in the turpentine, as it would tend to produce a greasy surface.
The same method of procedure is employed in coloring portraits as for landscapes. If you have previously experimented with landscape prints, the experience thus gained will make it possible for you to start on the background at once. If you have not practiced on the landscape prints, then it will be advisable to make your first experiments on plain manilla paper, selecting and blending colors that would be suitable for the background.
Prepare the stump according to the size of the background you intend to color. Dip it in turpentine and charge one side with one of the colors that you expect to use. Carry this to the slab. Then, using the other side of the stump, to avoid mixing the original stock colors, again charge it with another color, and place on the slab within an inch of the first. Mix these together and apply, in a hit or miss manner, to the portions of the background that you wish to cover. Do this as quickly as possible. Spread the colors over the entire background surface, in a circular motion, as rapidly as possible, before the turpentine evaporates. Then with a wad of cotton lightly rub the surface in a similar manner, until you get a smooth and uniform tint. Rub lighter on the portions that you wish stronger than others, while the more delicate and light ones should be rubbed harder. In this way the depth of tone is controlled, and at the same time an even blending supplied. Continue rubbing with this cotton until the turpentine has completely evaporated and the colors dried. No harm will be done if the colors should touch any object on the photograph other than the background, or if they overlap considerably, as corrections are easily made when you come to that portion. It makes no difference whether the print is too strong or too weak; alterations can be made as many times as necessary until the desired tone is obtained. After each application, however, the print should be evenly blended by rubbing lightly with dry cotton.
When the body tone of the background is completed, fill in the shadows and high-lights. As you approach the principal object or subject, the tint must be warmer, while toward the edge of the print it may be darker; much depending, of course, on the nature of the print. To make the background darker, take the wad of cotton that has been used in rubbing the background, dip it in a little of the color you desire, rub it over a piece of rough paper, and then apply where desired. For shadows or densest portions of the background charge a clean stump with the proper color, but before applying to the print remove the apparent greasi-ness by turning in a piece of cloth held between two fingers of the left hand. Work up the shadows with the stump in this condition until the proper strength is obtained, after which blend the deep shadows with the higher tones, using a large cotton stump. The light shades are obtained by rubbing the surface freely with the dry stump. It is not necessary to first cover the background with turpentine; just apply the color as mixed and dilute with turpentine. If the print does not take the color well another drop or two of oil in the turpentine will overcome this difficulty.
Coloring the Face. - If any of the background coloring has run over onto the face, it may be removed by rubbing the surface with a piece of soft, dry cotton, or India rubber; yet this is not necessary unless the background colors are extremely bright. Should any difficulty be experienced in removing the background color, it can be rubbed off with a clean cotton stump dipped in turpentine. The face can be colored with from three to five tints, three being sufficient for the beginner. The mixtures are composed of one or two colors, never more. It is easy to mix different colors, as their appearance when together will be your guide; so it is not necessary to have any previous knowledge regarding color combinations. Alterations of tints and shades can be made at will.
First Tint (Flesh Color). - Prepare a stump of a size proportionate to that of the face to be painted. Dip the stump in turpentine, slightly squeezing it between the first and second fingers, and with it carry some crimson and some yellow ochre to the palate or slab. Gradually mix until you get the desired flesh tint. The turpentine thins the mixture sufficiently so it can be easily and smoothly applied. Rub the stump over the face in a circular motion, as quickly as possibly, exercising no particular pains just so long as the surface is covered. This accomplished, immediately rub the surface lightly and in a circular motion with a soft linen rag doubled over the index finger. Do this until the color is quite dry and even. If for any reason the color is not sufficiently strong nor satisfactory, begin again, without removing the preceding tint, and add one color or the other until you obtain the natural tine. Remember, that when using a new stump it must be always dipped in turpentine, otherwise the cotton would absorb the colors, making it very difficult to apply them evenly to the print.