There are few processes in the art, which are as simple and easy to follow and capable of such beautiful results, as making prints on blue paper. As the paper is so easy to prepare, every amateur should make his own, because it is always better for being perfectly fresh. Any good close-grain, hard-surface, wove paper is good for our purpose, and the heavier the better. The best paper that the writer ever used for this purpose, was some very heavy paper especially prepared by Crane. A so-called book paper will not answer, as it is too porous. But any, paper that makes a good writing paper, will also make good blue paper. To prepare the paper, the amateur will need a very fine, soft sponge, one of those usually called a nursery sponge. For convenience in handling this, about half or two-thirds of the sponge should be inserted in the neck of a rather wide mouth bottle, which will serve as a handle. The part of the sponge outside the bottle should measure about one inch and a half in diameter, to be the proper size for applying the sensitizing solu tion. For the solution, procure several ounces each of citrate iron and ammonia and ferricyanide of potassium (red prussiate of potash) C. P. The chemically pure is very much to be pre ferred to the ordinary commercial article, because it produces a much more brilliant blue. Take of the latter 256 grains and dissolvein a four ounce bottle of water; cover the bottle with an opaque paper and label it, Red prussiate of potash. 1 dram equals 8 grains.
We make a stock solution of this because it will keep indef initely. The other chemical used in sensitizing blue paper will not keep, and therefore should be prepared fre,sh every time.
Having previously prepared this potash so that it will be dis solved and ready to use when needed, we dissolve 50 grains citrate iron and ammonia in one-half ounce of water. This takes but a few minutes to dissolve. The citrate of iron and ammonia should be kept in a wide-mouth glass bottle and corked tight, so that no air or moisture can get to it. Having the two chemicals now dissolved and ready to use, we pour into a small graduate four drams of the potash solution, which is the same quantity as we are going to use of the iron and ammonia. We place our funnel in our four ounce graduate, having previously placed in the bottom of the funnel a small wad of wet cotton wool, and pour the potash into the funnel and immediately follow it with the half ounce of iron and ammonia. They will filter through
the cotton in a few minutes, and to this solution we add about one grain of bromide of potassium from the stock solution which we have at hand. This bromide must be used judiciously. If all the paper is to be used within a week, do not add any brom ide. It is only to be added where the paper is to be kept for some uncertain•time. Too much bromide will make the paper print slowly. The object of this bromide is to keep the sensi tized paper fresh. Now take the paper which we wish to sensi tize, and cut it to a convenient size, as it is much easier to sensitize smoothly a small sheet of paper than it is a large one. We pin this paper by the four corners to a smooth board on which has been placed a sheet of clean paper. Any drawing board will answer for this purpose, if it is soft enough to hold the pins. Now we take the sponge and moisten the end of it, so that it will take water freely, and then squeeze all the water out of it, and dip the sponge in the sensitizing solution that is in the graduate. The sponge will suck up more than we need, so we press it against the glass to squeeze out a part. The quantity can only be learned by experience.* With the sponge in hand, now swab the paper gently, smoothly and quickly, beginning at the upper left-hand corner and brushing lengthwise across the paper, continuing this, always working the sponge in the same direction, until the surface of the paper is covered with the solution; then immediately, without again dipping the sponge in the glass, swab the paper at right angles to the first direction, be ginning at the lower left-hand corner and ending at the upper right-hand corner. This should be done quickly and smoothly. Hang the paper up to dry, by one or two of the pins, where no dust or dirt can get upon it, and proceed to sensitize another sheet in the same way. After sensitizing the quantity needed, the paper, which will dry in a few minutes, can be cut to different sizes. All of these operations, of course, should be done in the evening and not by daylight. If all of the solution is not used do not attempt to preserve it, but throw it away and care fully dean out the glass. So much for the paper.