. The silver sunbeam : a practical and theoretical text-book on sun drawing and photographic printing. e vessel. The solution willkeep good for a week, but must be filtered for use. The exposure is three times that of wet plates. The de-velopment may be by either neutral or alkaline pyro. 484 PROCESS FOR OBTAINING POSITIVES IN COLORS. Process for Obtaining Positives in Colors. The following is M. Niepce de St. Victors method forobtaining positives in colors: Red Color. Prepare the paper with a solution of nitrate of uranium,strength 24 grains to the ounce. Leave the paper fromfifteen to twenty
. The silver sunbeam : a practical and theoretical text-book on sun drawing and photographic printing. e vessel. The solution willkeep good for a week, but must be filtered for use. The exposure is three times that of wet plates. The de-velopment may be by either neutral or alkaline pyro. 484 PROCESS FOR OBTAINING POSITIVES IN COLORS. Process for Obtaining Positives in Colors. The following is M. Niepce de St. Victors method forobtaining positives in colors: Red Color. Prepare the paper with a solution of nitrate of uranium,strength 24 grains to the ounce. Leave the paper fromfifteen to twenty seconds upon this solution; then dry itbefore the fire, in the dark. Expose it in the pressure-frame from eight to ten minutes in sunshine, and from oneto two hours in the dark. Wash it for some seconds inwarm water (120° Fah.), and then immerse it in a solu-tion of red prussiate of potash, strength 10 grains to theounce. In a few minutes the print will acquire a beautifulblood-red color. Wash it in several changes of water, un-til the water remains perfectly colorless, and then dry it. Fig. Green Color. Take a red print obtained as before described. Im-merse it for a minute in a solution of nitrate of it without washing, and dry it before a fire; itwill become green. Fix it by putting it for a few secondsinto a solution of sulphate of iron, 20 grains to the ounce,and sulphuric acid 1 scruple to the ounce. Wash it oncein water, and dry it before the fire. Violet Color. Prepare the paper with nitrate of uranium, as in the redprocess. Expose it in the pressure-frame; wash it withwarm water; and develop the image with chloride of gold, PROCESS FOR OBTAINING POSITIVES IN COLORS. 485 2 grains to the ounce. When the print has acquired a fineviolet color wash it in several changes of water, and dry it. Blue Color. Prepare the paper with a solution of red prussiate ofpotash, 100 grains to the ounce; dry it in the dark. Re-move the print from the pressure-frame when
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