Blue paper should be printed preferably in the sunlight, as it may take several hours to print in the shade, and the printing should be continued until the dark portions of the picture assume a kind of bronze color. A little experience will show just how far to carry the printing. When the printing is done, the print should be placed in a tray of water, face down for a few minutes, and left there until the whites in the picture come out dear, or till the white margin around the picture comes out white, when it can be hung up to dry. It is not necessary, of course, to put the prints in the water, as soon as they are printed, as they can be kept for a day or two, and a number of them washed at the same time.
We think it is a very good plan in making blue prints to have one or two large frames, so that the blue print can be printed in the center of a large sheet of paper, when it will show like an engraving, with a broad margin around it. Suppose we have a frame, the inside of which is 11 x 14 inches, for which we have a piece of glass cut the same size, as a support to the smaller neg ative from which we wish to print in this frame. If our negative
is 5 x 8 inches for example, we cut out a sheet of thick opaque paper 11 x 14 inches and in the center of this, for a 5 x 8 neg ative, we cut an opening, say four and five-eighths inches one way and seven and a half inches the other way. Placing the neg ative in the center of our frame on the glass, we lay upon it this black mat, so that all the margin of the negative is entirely covered, and upon this we lay our sheet of blue paper, cut the same size, 11 x 14 inches. We make a print from this, and on putting it in the washing-tray, we find that all of the blue solu tion on the margin washes off, leaving all of the paper except the picture pure white. After it is dried, it should be pressed smooth under a heavy weight.
Plate marks can be made on these prints in the same way as described in the following chapter.