for blue process work. Some grades of brown Manila are very good; others
have little specks embedded in their surfaces which refuse to take on a
blue tint; still others, when printed upon, have white lines that are
wider than the corresponding black lines of the negative. The blue
obtained upon bond paper appears to be particularly rich, and the whites
remain pure; but bond paper cockles badly, and the cockles remain in the
finished print. Weston's linen record is an excellent paper. It is
strong, cockles but little, and dries very smooth. A paper that is used
by Allen & Rowell, for carbon printing, is comparatively cheap, and is
an excellent paper. It is not so stiff as the linen record, and the
whites are quite as pure. It does not cockle, neither does it curl while
being sensitized. It comes in one hundred pound rolls, and is about
thirty inches wide. The best papers are those that are prepared for
photographic work. The plain Saxe and the plain Rives both give
excellent results. Blue lines on a pure white ground can be obtained on
these papers, from photographic negatives, without difficulty. None of
the hard papers of good grade require the use of gum in the sensitizing
liquid. The liquid penetrates the more porous papers too far when gum is
not used, and without it good whites are seldom obtained upon porous
paper.

_The Best Chemicals for this Work_ are the _recrystallized_ red
prussiate of potash and the citrate of iron and ammonia, _which is
manufactured by Powers & Wightman_, of Philadelphia. If the red
prussiate has not been recrystallized, the whites will be unsatisfactory
and the samples of citrates of iron and ammonia which have come to us
from other chemists than those named, have all proved unreliable for
this process.

_The Sensitizing Liquid.--Its Proportions._--The blue process was