Platinum solution 12 parts
Chlorate of iron 11 parts
Distilled water 2 parts(21)
To obtain proofs not completely black, as, for example, reproductions of
lead drawings, the solution may be diluted with half or the whole volume
of distilled water. But if the solution be applied on little absorbent
surfaces or on paper strongly sized it is not advisable to dilute it.
_Preparation, of the Paper.—_The paper should be kept slightly moist in
order that it does not too completely absorb the sensitizing solution.
Therefore, when the atmosphere is very dry, it is well to keep the paper
in a damp place, in the cellar for example. Before sensitizing, which
should be done by a very diffused light, a quantity of the solution
proportionate to the surface to be sensitized (about 15 c.c., for a whole
sheet of Rives’ or Saxe paper) must be measured, and spread with a large
brush(22) on the paper fixed with drawing pins on a board covered with a
sheet of blotting paper. When well impregnated, the paper is hung up to
dry in the dark room, and as soon as the apparent dampness of the surface
has disappeared, it should be dried immediately at a temperature of 30—40
deg. C. (86—101 deg. Fahr). If the paper be dried too rapidly the
sensitive compound remains on its surface, and in developing the image
does not come out well. If, on the other hand, the drying is too slow,
the solution penetrates too much in the paper and the image is wanting of
vigor and does not appear very sharp. One cannot depart from this rule
that the desiccation from the moment the solution has been applied until
the paper is dry should last no more than from twelve to fifteen minutes.
The sensitized paper is hygroscopic and must be preserved in a calcium
box. _It is a conditio sine qua non that the paper must be quite dry
before, during, and after printing, to obtain good results._ Dampness is
the greatest enemy in this process.
For printing a pad of India rubber should be placed over the platinum
paper to prevent it from attracting the atmospheric moisture, and in damp
weather it is even advisable to cover it with several sheets of blotting
paper previously heated before the fire.
The platinum paper is at least three times more sensitive than the silver
paper used in the printing-out process, under the reductive action of
light the yellow color of the prepared paper turns brown and then becomes
of a lighter color, nearly orange, so that the darker parts of the image
often appears more luminous than the dark half tints. No rule can be
given to regulate the insolation, but after a few trials it is easy to
judge when it is right by observing the progress of the reduction and the
color of the image. The orange color indicates the complete reduction of
the ferric oxalate. When the details in the lights are _faintly_ visible,
the exposure is generally right.
The developer consists of an almost saturated solution of potassium
oxalate _acidified by oxalic acid,_ and for use heated to 80—85 deg. 0.
(176—184 deg. Fahr.),(23) in an agate glazed iron tray placed upon a water
bath at the above temperature. By simply drawing the proof over it, the
image is at once developed.(24)
When the proof is thought to be over-exposed, the oxalate solution can be
employed at a lower temperature. If, on the contrary, it is
under-exposed, the solution may be heated even to the boiling point.
The developer can be used over and over again. _It should always have an
acid reaction._
According to Mr. Borlinetto a sepia tone is obtained by using the
following cold developer:
Saturated solution of 120 parts
potassium oxalate
Saturated solution of 13 parts
copper chloride
Oxalic acid 1.5 part
After developing the proofs are _immediately_ immersed for fixing in a
solution of hydrochloric acid, 1 to 80 of water, renewed so long as the
paper is tinged yellow (about three times), leaving the proofs ten minutes
in each solution. Lastly, they are washed to remove the acid.
The platinotype has been still improved by Captain Pizzighelli, who
devised the following methods of operating by which the impressions are
obtained by the continuous action of light, that is, without development,
thus rendering the platinotype just as simple as the ordinary printing-out
silver process.
In these new processes to the sensitizing solution is added the alkaline
oxalate, which effects the reduction of the platinous salt during the
exposure to light. Consequently the prepared paper is insolated until the
image appears as it should be, or—which is exceedingly useful in cloudy
weather—until it is entirely visible but still deficient in delicate half
tones, for in the dark the action proceeds and the image developing itself
will be found finished in a period which may extend to a few hours. But
it can be, however, developed in a few seconds by immersion in a cold or
slightly warm solution of sodium carbonate, 1:25 of water. The image is
fixed as directed in the foregoing process.
The paper, prepared exactly as in the former process and kept in the
calcium box until wanted for use, should not be employed quite dry, but
allowed to absorb a little moisture by hanging it in the dark room.
Hence, the India rubber and other protecting pads can be dispensed with.
They are even objectionable, for dampness is absolutely necessary to
promote the chemical changes by which the image is developed.
A. AMMONIO-FERRIC OXALATE SOLUTION
Ferric oxalate solution 100 parts
Neutral ammonium oxalate 18 to 20 parts
B. SODIO-FERRIC OXALATE SOLUTION
Ferric oxalate solution 100 parts
Neutral sodium oxalate 15 to 18 parts
To prepare these two solutions the ammonium or sodium oxalate is dissolved
by small quantities at a time, and when the emerald color due to the
formation of the double oxalate commences to darken, the saturation being
then complete, no more of either salt should be added. The solution is
now well shaken with 3 parts of glycerine, allowed to settle and filtered.
Any one of the double oxalates can be used. The ammonium tends to produce
softer pictures and bluish tones. To obtain more contrasts a little
potassium chlorate may be added.
C. IRON CHLORATE SOLUTION
Solution B 100 parts
Potassium chlorate 0.4 part
D. MERCURIC SOLUTION.
Mercuric chloride 20 parts
solution at 5:100
Sodium oxalate solution 40 parts
at 3:100
Glycerine 2 parts
SENSITIZING SOLUTIONS.
FOR BLACK TONES.
Platinite solution, 1:6 5 parts
Solution B 6 parts
Solution C 2 parts
FOR SEPIA TONES.
Platinite solution, 1:6 5 parts
Solution C 4 parts
Solution D 4 parts
Intermediate tones are obtained by diminishing the dose of C and replacing
it by an equal volume of B. For this process the paper should be sized
with
Arrowroot 2 parts
Sodium oxalate at 3:100 100 parts
To dispense with this preliminary sizing Captain Pizzighelli adds gum
arabic to the platinite solution, whereby the sizing and sensitizing are
done in one operation.
The gum arabic solutions are prepared as follows:
E. Gum arabic in 40 parts
powder
Sodium ferric 40 parts
oxalate solution,
B
Sodium oxalate 100 parts
solution at 3:100
Glycerine 3 parts
Place the glycerine and the gum arabic in a mortar, then, stirring with
the pestle, dissolve by adding, little by little, the mixture, heated to
40—45 deg. C. (104—113 deg. Fahr.), of the solution of sodium ferric
oxalate and sodium oxalate. Let stand for about two hours and grind again
to dissolve entirely the gum arabic. Filter through muslin.
F. Mercuric chloride 20 parts
solution, 5:100
Sodium oxalate solution, 40 parts
3:100
Gum arabic in powder 24 parts
Glycerine 2 parts
Dissolve as said above.
SENSITIZING SOLUTIONS.
FOR BLACK TONES.
Platinite solution, 1:6 5 parts
Solution E 6 parts
Solution C 2 parts
FOR SEPIA TONES.
Platinite solution, 1:6 5 parts
Solution C 4 parts
Solution F 4 parts
Mix just before use. The solutions do not keep. The paper prepared by
either one of these two processes can be exposed as in the _old_ process,
and the image developed bythe hot oxalate solution.
The preparation of wood, canvas, etc., for the platinotype printing need
not to be described; it suggests itself.