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.
Sizing The Paper. If the worker is not satisfied that the paper he is going to use is well sized, it is best to make a test. This can be done by mixing up a small quantity of bichromate, gum solution and a little color, and applying it with a brush to a strip of paper. Let it dry in the dark, and when dry immerse it in cold water. If after a time the color comes off entirely, leaving the paper pure white, the paper is suitable for coating. If, however, a color stain is left on the paper, which cannot be washed out, it is proof that the paper is not sufficiently sized.
435. To size paper prepare a sizing solution consisting of 31 grains of arrow-root in 1 quart of water. Bring the water first to a boil, then add the small quantity of arrowroot. Set to cool and then place in a bottle. Apply the sizing to the paper with a flat brush. One or two coatings should be sufficient. A weak gelatin size can be given to the paper by dissolving in a suitable vessel or bottle, 90 grains of Nelson's Gelatin No. 1 in 10 oz. of water. The gelatin should be allowed to swell in the water first, and then dissolved by placing the vessel containing the gelatin in a dish of hot water. An ounce of alcohol can then be added. This gelatin size is applied to the surface of the paper in the same way as the arrow-root size.
Choice Of Two Methods. There are two methods of preparing the sensitized paper. In the first the paper is brushed over with the bichromate solution, or immersed in it, and hung up to dry, then stored away in the dark, the gum and pigment mixture being added later. In the other method the gum and color are added to the bichromate solution and the paper coated in one operation. This method is advisable for the beginner.
437. Method No. 1. In a room that is slightly darkened stretch a sheet of paper over a clean blotter on a board or table. Hold the paper down at the corners by push pins or thumb tacks. Pour a small quantity of your bichromate solution in a saucer or graduate, and with a bristle brush apply it over the surface of the paper, covering it thoroughly and evenly. The stroke should be applied from right to left, across the paper, then up and down and across. As each sheet of paper is sensitized hang it up to dry by little wooden clips, or over a string stretched across the room. When such sensitized paper is desired for use, prepare a mixture of gum solution and pigment, in about the following proportion: Pour half an ounce of gum solution on your glass plate, and then add as much lamp black as will cover a ten cent piece. Also add the same quantity of ivory black.
438. With your palette-knife mix the gum and color intimately. If tube colors are being used, squeeze out about one-half inch of color of each of the lamp black and ivory black. When the solution is thoroughly mixed it should be of somewhat denser consistency than water, but should not be too thick, as it will be difficult to coat on to the paper. If too thin the image will be thin and weak. If you find the mixture is too thick, you can thin it by adding a little water, or if too thin, you can add a little gum solution and some more color. With your second bristle brush apply this color to a sheet of the previously sensitized paper in the following manner: Take a sheet of paper somewhat larger than the size of print you desire to have. Stretch it on a board with push pins, having the push pins on the right-hand side inserted loosely, so that when the paper buckles (as it will when the solution is applied) it can be quickly drawn out tight again.
439. With your bristle brush full of color apply the mixture to the center of the sheet of paper, then with quick strokes, spread it right and left and up and down. This must be done quickly, as the mixture sets very rapidly, and once it is set all hope of even blending is gone. As soon as the color has been applied to the sheet, take up your blending or spreading brush and, holding it perpendicularly in your hand, pass lightly over the surface of the color, from right to left, up and down, and from corner to corner, as quickly as possible, dragging the points of the brush over the color, which helps to blend the bristle brush strokes.
440. Some little practice will be required to obtain a perfect, even coating. The moment that you see the blender beginning to make streaks in the color you must stop blending, for the more you blend the more streaky the coating will become, and these streaks will show in the finished print. The whole secret of good results in gum-bichromate printing is in the laying of the color on the paper, the thickness of the color, and the even blending; therefore, as both paper and coloring matter are inexpensive, it is a good plan to acquire a little experience in coating and blending color on paper.
441. Method No. 2. - This method is the one advised for the beginner. First prepare your combined sensitizing and coating mixture. For this purpose pour half an ounce of gum and half an ounce of bichromate solution on the glass plate, and add the amount of color given in the previous paragraphs. It will be found later, that certain colors require to be used in larger quantities than others, in order to obtain the correct thickness of coating. Blend the mixture thoroughly on the plate, by using the pallette-knife. It is better to use a small mortar and pestle, grinding up the solutions and the color until a perfectly smooth mixture is obtained.
442. If of the right consistency the mixture will drop off the end of the pestle in slow, thick drops. With the paper stretched on a board, over a clean blotter, and with the pins on one side loosely inserted, so that they can be removed quickly to stretch the paper, fill your bristle brush with the color and apply to the center of the sheet, in precisely the manner given in the previous paragraph. The coating of the paper and the blending must take place within one minute. The worker is advised to begin on a sheet not larger than 8x10. The paper when coated and blended should then be hung up by the corners to dry, a darkened room or cupboard being used for the purpose.