PHOTO TRACINGS IN BLACK AND COLOR.


Two new processes for taking photo tracings in black and color have
recently been published--"Nigrography" and "Anthrakotype"--both of which
represent a real advance in photographic art. By these two processes we
are enabled for the first time to accomplish the rapid production of
positive copies in black of plans and other line drawings. Each of
these new methods has its own sphere of action; both, therefore, should
deserve equally descriptive notices.

For large plans, drawn with lines of even breadth, and showing no
gradated lines, or such as shade into gray, the process styled
"nigrography," invented by Itterbeim, of Vienna, and patented both
in Germany and Austria, will be found best adapted. The base of this
process is a solution of gum, with which large sheets of paper can be
more readily coated than with one of gelatine; it is, therefore, very
suitable for the preparation of tracings of the largest size. The paper
used must be the best drawing paper, thoroughly sized, and on this the
solution, consisting of 25 parts of gum arabic dissolved in 100 parts of
water, to which are added 7 parts of potassium bichromate and I part of
alcohol, is spread with a broad, flat brush. It is then dried, and if
placed in a cool, dark place will keep good for a long time. When used,
it is placed under the plan to be reproduced, and exposed to diffused
light for from five to ten minutes--that is to say, to about 14 deg. of
Vogel's photometer; it is then removed and placed for twenty minutes in
cold water, in order to wash out all the chromated gum which has not
been affected by light. By pressing between two sheets of blotting-paper
the water is then got rid of, and if the exposure has been correctly