Prussiate of potash, 60 grains.
2d.—Water, 1 ounce.
Ammonia citrate of iron, 70 grains.
When these are dissolved, mix them together, and pour them through a piece of filter-paper into a tumbler, and then into a clean glass bottle. If filter-paper cannot be had, nice clean cotton wool answers the purpose nearly as well. This solution should be kept and also used in a dark room. To sensitize the paper, pour out a little of the liquid into a saucer; then having cut note-paper into rectangular pieces, a trifle smaller than the glass in your frame, take one of these pieces at a time, and place it evenly upon the surface of the liquid; let it lie in this position until it is flat and not inclined to curl. Now take it out by one corner, and thrusting a pin through this point, drive it lightly into the edge of a shelf in your dark room, and leave it to dry. It is now ready for use; should any be left after printing, roll it up and place it in a tin box which has a cover, to keep it from the light and dampness. To print on this paper, place your glass in the frame, and next to it any engraving you may fancy, provided it is printed on thin paper and has no type on its back. If a copy is desired precisely like the original, place the engraving face downward on the glass, but if a reverse is wished, that is, one in which all the objects in the original are turned about, and its left side is to correspond to the right in your print, then place it with its face toward you in the frame. When this is adjusted to your satisfaction, take the frame to your dark closet, and put in your sensitized paper, being careful to cover it closely with the back of the frame well fastened in place before bringing it to the light. Place the frame, glass side upward, on a window-ledge, or in any place where it will be exposed to the free rays of the sun, and let it remain until it is printed to the desired depth. It will be noticed that at first the light changes the portions exposed to a bluish color; the operation, however, is not finished at this stage, but must be continued long enough to turn these portions a deep metallic gray. Care must be exercised in examining the print, that the paper is not moved from its position relative to the copy to be printed; with the above frame this will be a very delicate matter, and it is doubtful if it can be successfully done. A better way would be to make one or two prints, without caring for accuracy of form, but simply with a view of obtaining a good color, and time the operation; this would form a sort of basis from which to work. If some subsequent engraving was upon thicker paper, it would take a somewhat longer time to print it, and if on thinner paper, the time required would be proportionately shorter. It would be a great source of convenience if the back could be cut in two equal parts, and a piece of canton flannel be pasted over both, joining them as they were at first. This with the soft side outward will keep the paper from slipping, and act as a hinge to either half. Now instead of one fastening, two will be required, one on either half of the cover; if then you wish to examine your print, you have only to open one end of your frame, and carefully lift up the edge of the paper, while the other end, remaining firmly closed, holds the whole thing in place.
After your print has reached the proper degree of color, take it out and immerse it in clean water, when it will become a rich blue, except those parts which are to remain white. Change the water once or twice, or until every part comes out distinctly; then take it from the bath and dry between sheets of blotting-paper.
The second way to prepare paper consists in washing good letter-paper with the following solution:
Bichromate of potash, 10 grains.
Sulphurate of copper, 20 grains.
Water, 1 ounce.
Papers prepared with this are of a pale yellow color; they may be kept any length of time in a tin box, and are always ready for use. For copying engravings, the wings of dragon-flies, or of cicadas, the beautiful skeletonized leaves or delicate ferns, arranged in tiny bouquets on the inner surface of the ground glass, this paper is excellent.