> The paper, calendered or not,(18) is sized with gelatine or arrowroot.

The color of the proof with the latter size is brownish black, and bluish

black with the former.



To prepare the gelatine solution 10 parts of gelatine are soaked in 800

parts of water and then dissolved at a temperature of 60 deg. C. (140 deg.

Fahr.), when 200 parts of alcohol and 3 parts of alum are added and the

solution filtered.



To prepare the arrowroot solution 10 parts of the substance are powdered

in a mortar with a little water and mixed to 800 parts of boiling water,

added gradually in stirring. After boiling for a few minutes 200 parts of

alcohol are added and the mixture filtered.



These solutions are employed warm. The paper is immersed for two or three

minutes and hung up to dry in a heated room, then immersed a second time

and dried by hanging it up in the opposite direction, in order to obtain

an even coating.



The potassic platinic chloride is an article of commerce. It should be

soluble without residue in 6 parts of water and without acid reaction. In

this proportion it constitutes the normal stock solution employed in the

various formulas.



The standard ferric oxalate solution is also found in commerce. Treated by

potassium ferricyanate it should not be colored blue, nor become turpid

when diluted with one-tenth part of water and boiled. The former reaction

indicates that it contains no ferrous salt, and the latter no basic

oxalate.



The authors give the following instructions for preparing the ferric

oxalate solution, to which they attach much importance:



Five hundred parts of ferric chloride are dissolved in 5,000 parts of

water and heated to boiling, when a solution of soda is added until the

liquid becomes alkaline.(19) About 250 parts of caustic soda are generally

employed for this purpose. The precipitate--ferric oxide--is now washed in

warm water until the last washing water is quite neutral to test paper,

then drained and mixed with 200 parts of pure crystallized oxalic acid.

The mixture is then allowed to stand in the dark for several days at a

temperature not exceeding 30 deg. C. (86 deg. Fahr.) At first the

solution from green turns to a yellow green, and finally becomes almost

brown. At this moment the excess of ferric oxide is filtered out and the

liquor submitted to a quantitative analysis, the result of which leads to

ascertain the quantity of ferric oxalate in 100 parts of the solution and

the excess of oxalic acid. The solution should then be diluted with

distilled water, such as it contains 20 parts of ferric oxalate per 100

parts of water, and oxalic acid must be added in the proportion of from 6

to 8 per 100 of the ferric oxalate, taking into account the quantity of

acid the solution already contains. The solution should be kept in the

dark. It is altered by light.(20)



IRON CHLORATE SOLUTION

Ferric oxalate solution 100 parts

Potassium chlorate 0.4 parts



This solution is employed to obtain more contrasts.



PREPARATION OF THE SENSITIZING SOLUTION

Platinum solution 12 parts

Ferric oxalate solution 11 parts

Distilled water 2 parts



This solution gives very soft tones with intense black. To obtain more

brilliancy we use the following proportions:



Platinum solution 12 parts

Ferric oxalate solution 9 parts

Chlorate of iron solution 3 parts

Distilled water 2 parts



To obtain results comparable to those which the silver printing out

process gives, the following mixture is employed:



Platinum solution 12 parts

Ferric oxalate solution 8 parts

Chlorate of iron solution 4 parts

Distilled water 8 parts



For very weak negatives, reproductions of drawings, etc., we use--



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.