This section is from the book "Modern Photography In Theory And Practice", by By Henry G. Abbott. Also available from Amazon: Modern photography in theory and practice: A hand book for the amateur.
Hydrochloric Acid............................................ 1 dram
Water.......................................................... 10 ounces and after allowing it to remain there a few minutes remove and again thoroughly wash it in running water, when it can be dried.
In the above formula we spoke of a 2 per cent solution of nitrate of silver and such expressions are often found in books on photography without any accompanying explanation and this makes it very confusing to the amateur, as it may be understood by him in various ways. Ordinarily among photographers, a 10 per cent solution of bromide is understood to consist of 9 ounces of water and 1 ounce of bromide. This from a chemist's standpoint is all wrong and is not a ten per cent solution by any means. Soluble salts are taken up by water without increasing the bulk and we might take 10 ounces of water and stir into it 1 ounce of bromide without perceptibly elevating the level of the water. Suppose we want to make a 2 per cent nitrate of silver solution and the total amount of solution required is 10 ounces, then we will proceed as follows: One ounce contains 480 grains and 10 ounces will contain 480 multiplied by 10, or 4,800 grains. Two per cent of 4,800 grains is 96 grains and we would therefore weigh out 96 grains of silver and dissolve it in 10 ounces of water. Blue print paper can be purchased very cheaply on the market but it does not keep well for any great length of time and the amateur might like to experiment in making his own paper, which he can easily do as follows: Secure some sheets of good wove linen paper, or any other paper having a smooth surface which is fairly heavy. Any good writing paper without the lines, or what is known as laid water marks in it, will be found fit for the purpose. This paper should be held firmly to a drawing board and the surface coated with the following solution:
Citrate of Iron and Ammonia, 50 grs. Water....................4 drams.
Red Prussiate Potash ...... 32 grs,
Red prussiate of potash is also known as ferricyanide of potassium, and these chemicals should all be what is known as C. P., or chemically pure. Now pour into a graduate the 4 drams of No. 2 and filter into a bottle by placing a plug of cotton in the bottom of the funnel or by means of filter paper. As soon as this is filtered immediately follow it with the 4 drams of No. 1, and add a small quantity of bromide of potassium from the stock solution. This bromide is added in order to make the paper keep but if it is to be used at once the bromide may be left out. The solution is applied to the face of the paper by means of a very soft sponge or what is known as a Blanchard brush. This brush is easily made by taking a small strip of glass or wood, say two inches wide by six long, and fastening over the end of it several thicknesses of cotton flannel holding it in position by means of a rubber band. If a sponge is used a small stick should be tied to it for a handle, or it may be mounted by securing a small piece of glass tubing, say four inches long by one inch in diameter. Loop a piece of hard twine around the sponge and pull the two ends of the string up through the glass tube and fastening them there. A small quantity of the solution should be taken on the brush or sponge and the paper lightly brushed from left to right, starting at the top, until you have reached the bottom of the sheet. Now turn the board around so that the lines we are about to make will cross the others at a right angle and proceed to go over the sheet in the opposite direction. In this way you avoid streaks on your paper by filling in places in the. second application that were missed in the first. Your paper can now be pinned up or hung up in the dark room to dry. The operation of sensitizing blue print paper can be done by lamp light but if performed in the day time the operation would have to be confined to the dark room or some place devoid of daylight. As soon as the paper is dry it can be cut up in sizes to suit and packed away carefully in strong light-tight envelopes.
In sensitizing for blue prints you will have to prepare your solutions somewhat differently for different papers, as a less amount of iron and ammonia will be required on soft than a hard paper. Very beautiful effects may be secured with blue prints by sensitizing light blue writing paper, the result being a dark blue print on a light blue ground. Other shades of paper may be selected but care must be exercised that the colors of the paper are permanent and will not wash out when we come to wash our prints.
Blue prints may be used advantageously for sketching with India ink for making book illustrations, decorating menus, etc. A blue print is first made from a negative of the article which you wish to illustrate. This print is washed in water and dried. Now with waterproof India ink, Higgins', or any other, proceed to draw in over the blue lines and when the drawing is finished bathe it carefully in a weak solution of potash and water. A weak solution of condensed lye and water will answer very well. Under the action of the potash solution the blue will be dissolved and run away, leaving the waterproof lines behind. The print should then be washed carefully in several changes of water and dried and you will have a clean-cut black drawing on a white ground, which will reproduce nicely in the zinc etching process. Fig. 35, and other illustrations in these pages, are produced in this manner.