The Cyanofer Pellet's Process
This process gives blue impressions on a white ground from positive
cliches, and white impressions on a blue ground from negative cliches.
It is termed "positive ferrotype process."
The cyanofer is an application of one of the numerous and useful
inventions for which photography is indebted to A. Poitevin. In 1863 he
discovered that certain organic substances were rendered insoluble by
ferric chloride, a
influence of light the ferric chloride has been reduced to a ferrous salt.
This curious phenomenon is the base of the process now to be described.
As usual the process has been modified by compounding the sensitive
solution in various ways and by minor details in the manner operating.
But although these modifications have rendered the process easier to work
with, there is not a great difference in the results obtained. We give
two formulas. Aside from the addition of gum arabic, which was suggested
by Mr. Pellet, and which constitutes the capital improvement of the
process, the formula is substantially that devised by Mr. Poitevin.
Prepare three solutions as follows:
A. Gum arabic, best 50 parts
quality
Water 170 parts
B. Tartaric acid 12 parts
Water 80 parts
C. Ferric chloride 35 parts in volume
solution at 45
deg. Baume
Mix gradually B to C, then C, by small quantities, in agitating briskly.
It is important to prepare the solution as directed, for by adding the
ferric chloride before tartaric acid, the gum arabic would be at once
coagulated. When the ferric chloride is mixed, the solution at first
thickens, but becomes sufficiently fluid for use in a certain period. It
does not keep, and should be employed the day it is made if possible.
The paper, which should be well sized and calendered, and which, when not
giving good results by too much absorbing the sensitive solution, must be
starched as before directed, is coated either by brushing or by floating.
By the first method a roll of paper five yards long can be prepared
without great trouble, and give, perhaps, better results than if prepared
by floating; but the latter method is by far the the most convenient: one
does not generally prepare by brushing sheets of paper larger than about
30x40 inches.
For brushing, the paper is pinned on a board, then, with a large badger
brush dipped in the sensitive solution, the latter is applied as evenly as
possible; after which, by lightly passing the brush over, the striae are
removed, the coating well equalized, and the paper hung up to dry. The
coating should not be very thin, and, above all, not too thick, for then
it would require an unusually long exposure to allow the light acting
through the whole thickness of the film, which is a sine qua non to obtain
a clear ground, i.e., not stained blue.
To prepare by floating, pour the solution in a shallow tray, which needs
not to be more than 20x34 inches, 30 inches being the width of the drawing
paper usually employed; then roll the paper and place it on the solution.
Now, taking hold of it by two corners, draw it out slowly: the paper will
unroll by itself. This operation can be done by diffused daylight, but,
of course, the paper should be dried in a dark room. It dries rapidly.
Endless rolls are prepared by machinery. To expose, the drawing is placed
in the printing frame, face downwards, and the sensitive paper laid over
it. The whole is then pressed into contact by interposing a cushion
between the lid of the frame and the paper, and exposed so that the rays
of light fall perpendicularly upon it.
The cyanofer preparation is quite sensitive. From half a minute to two
minutes exposure, according to the intensity of the light and the
thickness of the coating, is sufficient in sunshine to reproduce a drawing
made on the ordinary tracing paper. In the shade, by a clear sky, the
exposure is about five times longer, and varies from half an hour to an
hour and more in cloudy weather, but then the design is seldom perfectly
sharp.
The progresses of the impression is followed by opening one side of the
printing frame and examining the proof. The exposure is sufficient when
the paper is tinged brown on the parts corresponding to the ground of the
design. The image appears then negative, that is, yellowish on a tinged
ground.
Another and more safe method of ascertaining the correct time of exposure,
which can be employed concurrently with the other, is to place a few
strips of the same sheet of sensitive paper between the margin of the
design, upon which a few lines have been traced, and the paper, and,
without opening the frame, to draw one of them, from time to time, and dip
it in the developing solution. If the whole strip be tinted blue, the
proof is not sufficiently exposed; but if the lines soon appear with an
intense coloration on the yellowish ground of the paper, and the latter do
not turn blue in a minute, at the most, the exposure is right. By excess,
the lines are with difficulty developed or broken.
For developing, we provide with three wooden trays lined with lead or
gutta-percha, or, more economically, coated with yellow wax. The wax is
melted, then applied very hot, and, when it is solidified and quite cold,
the coating is equalized with a hot iron, whereby the cracks produced by
the contraction of the wax when cooling are filled up.
One of these trays should contain a layer, about three-quarters of an inch
thick, of an almost saturated solution of potassium ferrocyanate (the
developer); the next be filled with water, and the third with water
acidified by sulphuric acid in the proportion of three per cent. in
volumes.
All this being ready, the margin of the proof is turned upwards--so as to
form a disk of which the outside is the impressed surface--in order that
the ferrocyanate solution does not find its way on the back of the proof,
which would produce stains. Now the proof is laid, the lower edge first,
on the developer, and gradually lowered upon it, when, taking immediately
hold of it by the two corners nearest to the body, it is lifted out and
held upright to allow one following the development of the image; and,
presently, if any air-bubbles are seen on the proof, they should at once
be touched up with a brush wetted with the ferrocyanate solution; the
reason explains itself.
The image appears at once. As soon as the fine lines are well defined,
the blue intense, and, especially, when the ground has a tendency to be
tinged blue, the proof is placed in the tray filled with water and in this
turned over two or three times, when it is immersed in the diluted
sulphuric acid. In this bath the print acquires a deep blue coloration,
consisting of Prussian blue, and the ground becomes tinted with a blue
precipitate without adherence, which is easily washed off by throwing the
liquid on the proof with a wooden spatula, or, better, by rubbing with a
rag tied to a stick. When the ground is cleared, and after three or four
minutes immersion to dissolve the iron salts acted on, the proof is rinsed
in water several times renewed to free it from acid, and hung to dry.
There are two causes of failures in this process, viz., over and
under-exposure. In the former case the fine lines are broken or washed out
in clearing the proof (which may also arise from the drawing made with an
ink not opaque enough); in the latter the ground is more or less stained.
The blue stains, the lines for corrections, etc., are erased with the the
potassic oxalate (blue salving, as it is termed) whose formula has been
given.
The additions, corrections and writing are made with a Prussian blue ink
prepared by mixing the two following solutions:
A. Ferric chloride, 4 parts
dry
Water 350 parts
B. Potassium 15 parts
ferrocyanate
Water 250 parts
The precipitate being collected on a filter and washed until the water
commences to be tinged blue, is dissolved to the proper consistency in
about 400 parts of water. This ink does not corrode steel pens.
It has been stated that the cyanofer process keeps for years if preserved
from the combined action of dampness and the air. The writer found in his
practice that the ferric salts in presence of the organic matters (the
sizes) acts as does potassium bichromate and renders, in a certain period,
the cyanofer film insoluble even after a prolonged insulation. Paper
freshly prepared is always more sensitive and gives better whites and
generally finer results.(10)
The prints can be toned black in operating as in the cyonotype, but the
results are seldom good.
Captain Pizzighelli's formula is as follows: Prepare
A. Gum arabic 15 parts
Water 100 parts
B. Ammonia ferric 45 parts
citrate
Water 100 parts
C. Ferric chloride 45 parts
Water 100 parts
For sensitizing mix in order:
Solution A 100 parts
Solution B 40 parts
Solution C 20 parts
The mixture very much thickens at first, but becomes sufficiently fluid
for use in a few hours. It keeps well for two or three days. Leaving out
B and replacing it by rain water, this makes also a good solution for the
cyanotype.
More
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A Poitevin's Process 1870
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