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.
Any kind of a picture can be colored - photographs on bromide paper, gelatin paper, platino or matt surface collodion paper, carbon, platinum, velox (or any gaslight papers), even engravings, drawings, etc., or prints on any kind of paper, glass or other material. The principal requirement is to have the surface so prepared that the turpentine cannot penetrate it. Any surface that will absorb turpentine must be covered with a hot liquid gelatin.
Papers That Will Not Need Coating. - Any collodion paper having a matt surface, such as aristo platino; or any gaslight paper such as velox, azo, argo, artura, etc.
Preparing the Gelatin for Use. - Make a 5 per cent. solution of gelatin; usually two strips of gelatin, about 4x5 inches, dissolved in a glass of water, will be sufficient. First, place the gelatin in a vessel of cold water, to remove any particles of dirt that may have gathered. It is advisable to change this water two or three times, when the gelatin should be covered with a half pint of warm water, the temperature of which need not exceed 100° - just hot enough to melt the gelatin. As soon as dissolved filter the gelatin through a piece of linen cloth into an ordinary glass tumbler. It is now ready for use.
Although seldom necessary to re-gelatinize any collodion or glossy gelatin paper, yet when heavy coloring is required it is preferable to re-gelatinize the print, but before doing so its surface should be made dull. To accomplish this apply pumice powder with a piece of cotton flannel, rubbing in a circular motion until the entire surface is dull. Then dust carefully with a soft camel's hair brush, when the print is ready for coating. After deadening the surface of highly glazed papers with pumice powder, it is advisable to rub the print lightly with a soft cloth, after which the gelatin may be applied. All matt surface prints should be first coated with glycerine before the application of gelatin.
Applying the Gelatin. - Gelatin is applied with a flat brush (Badger hair), and this must be done quickly with even strokes. If the strokes are started lengthwise of the print they must be continued that way. See that all portions of the surface are fully covered. If the gelatin has a tendency to draw on the brush - dragging and leaving lines - which would be the case if not quickly applied, as the gelatin sets rapidly, it would be better to use a weaker solution of gelatin and make two applications. In either case care must be exercised that a clean sweep be made with the brush the full length or width of the print. Never stop in the middle. To see if you have evenly coated the paper, hold the print before the light and look through it. The parts that are not completely coated can be gone over again. When coated hang the print up to dry; this should not require more than fifteen minutes.
Preparing the Stump. - The preparing of the cotton stumps is perhaps more difficult than some of the other features of this process, as the point of the stick must be completely covered with the cotton. A few trials, however, will make one a master of this. The required sizes of stumps vary according to the details of the work. When a different size stump is desired all that is necessary is to withdraw the former piece of cotton and discard it, and from a clean piece make another stump. This can be instantly done after a little practice.
To prepare the stump, sharpen the wooden stick to a very fine point. Do this by laying the end of the stick upon a piece of sand paper, so the taper of the point blends back at least two inches. The taper of an ordinary wooden knitting-needle is about 3/4 of an inch, but as this is too abrupt it will be necessary to make a sharper point by rubbing down with the sand paper. Illustration No. 108 shows the taper required.
Now place a small piece of absorbent cotton on the index finger of the left hand, permitting it to extend to the tip. Place the thumb on the cotton, at the base of the finger, to hold the cotton in position. Then, take the wooden needle and, holding it perpendicularly, rest the point on the end of the finger, in the center of the fine fibres of cotton. Commence rolling the stick or needle towards you. The constant rolling will gather up the cotton. Continue to turn the needle or stick until the cotton takes a good hold; then slightly lift the stick from the finger, permitting the cotton to roll in a ball over the tip until you come within 1/4 of the end of the cotton. Allow this end to roll up along the stick. This will hold the cotton secure to the stick, at the same time preventing ragged edges. The point of the needle must not project through the cotton - the wood must be fully protected. The smaller the stump the greater should be this precaution. Considerable time should be devoted to this practice, as much depends upon the proper stump. Illustration No. 108 gives an idea of the different shapes of correctly made stumps.
Illustration No. 108. Stump.
Before preparing your colors provide a little vial or dish to hold turpentine - a small butter plate will serve very nicely. Pour into this little dish about 1/2 ounce of turpentine. If you are to color platinum prints it will be necessary to mix a little poppy or linseed oil with the turpentine - a few drops will be sufficient. For collodion or gaslight papers the plain turpentine should be used, as the oil is unnecessary. Having prepared the turpentine distribute the colors on the slab or plate.
To mix the colors for special tints first squeeze a small portion of the oil color from each tube onto the plate, placing the colors about 2 inches apart. Mix the colors as you require them; for example, if you want a green, first moisten the stump with turpentine, dip into the yellow and carry it to a clean portion of the slab; next dip into the blue and place it within an inch of the yellow, then mix the two together. By using a little more of one than the other a lighter or a darker tone may be obtained. If the color is too heavy (thick), add a little more turpentine. After mixing the green prepare any other colors required, instruction for which has already been given.