Erasures on photographs of specimens should be made very carefully with a hard rubber that is free from sand, and the parts not to be disturbed should be protected with a shield. High lights may be added by carefully scraping or rubbing the surface of the paper.
LANDSCAPE DRAWINGS FROM POOR PHOTOGRAPHS.
A poor photograph or one that has become injured and can not be retouched for direct reproduction can be utilized by making from it, as described below, a pen drawing or a brush or crayon drawing, which will be almost photographically correct.
PEN DRAWINGS MADE OVER PHOTOGRAPHS.
A pen and ink drawing may be made over a blue print or a bromide print (preferably a blue print) and the photographic image then bleached out. The blue print should be larger than publication size and should not be so dark that the draftsman can not see his lines. If the negative is available a bromide enlargement can be obtained; otherwise the picture should be rephotographed in larger size, preferably twice publication size. The enlargement will give the draftsman greater freedom in drawing details and will make his work appear finer and better in the reduced illustration. If the photographic print is of a subject requiring the use of instruments it should be securely fastened to a drawing board, square with the board, so that any horizontal and vertical lines in it may be ruled by the use of a T square and triangle. For specimen or landscape work it need not be fastened.
For bleaching blue prints a saturated solution of oxalate of potassium (K2C2O4 + H2O) has been used with good results. For bleaching bromide prints cyanide of potassium (KCN) to which a few drops or flakes of iodine have been added should be used. Neither kind of print should be bleached until the drawing has been completely finished in every detail, because bleaching loosens the fibers of the paper, so that the ink of any added lines is likely to spread. The print should be placed in a hard-rubber pan, the bleaching solution poured on it, and the pan rocked until the image disappears. The print should then be carefully removed, thoroughly washed in running water, placed between clean white blotters to dry, and finally mounted on cardboard. For temporary, hurried work on drawings that are not to be retained for future use the blue print may be mounted first and bleached by pouring the bleaching fluid over the mounted print.
BRUSH DRAWINGS FROM POOR PHOTOGRAPHS.
Brush drawings may be made directly from photographs by working over an enlarged print with gouache, or by making a pencil tracing and sketch of the photograph and working it up with lampblack or india ink. The photograph should be larger than publication size to permit greater freedom and breadth in drawing details. The larger size will also afford a more refined and better engraving when reduced. If lampblack or india ink is used and the subject is small, bristol board is recommended, but if the photograph is larger than, say, 8 by 10 inches, Whatman's hot-pressed double elephant or similar paper, laid down with thumb tacks, will prove satisfactory.
If gouache is used over a print a preliminary drawing is of course unnecessary, but the photograph should be an unglazed print of a size that will require considerable reduction, and the finished drawing should be protected by an oversheet. If lampblack or india ink and not gouache is used the photograph should be traced and a fairly complete pencil sketch should be made before the brush is used.
Plates I, IV, A, V, B, and VII, B, Monograph 34, were made from gouache drawings. Plates III, A, VII, A, X, XI, XII, XIII, XX, XXVIII, and XXX, in the same publication, were made from lampblack or india-ink wash drawings. The originals can be examined at any time.