Improvements relating to the Sensitizing and Relative Sensitive Adjustment of Photographic Plates or the like for use in Color Photography and to the Measurement of Time Exposure of said Plates.
Year: 1899

page_text: Date of Application, 15th June, 1899
Complete Specification Left, 12th Apr., 1900-Accepted, 14th July, 1900
PROVISIONAL SPECIFICATION.
Improvements relating to the Sensitizing and Relative Sensitive
Adjustment of Photographic Plates or the like for use in Color
Photography and to the Measurement of Time Exposure of said
Plates.
I, GUSTAV SELLE, of Brandenburg on the Havel, in the Empire of Germany,
Physician, do hereby declare the nature of this invention to be as follows:-
In 3 color photography the sensitive plates for the 3 necessary negatives must
be constituted so that each shall be preponderatingly sensitive to the light rays
passing through the particular light filter behind which it is exposed, the
ordinary monochromatic silver plate being extremely sensitive to the rays con-
tained in the spectral section F to H requires no special treatment; on the
other hand the plates for the green and the red rays must be color sensitised,
i.e. must be rendered particularly sensitive to these rays respectively. Further
the color sensitiveness must be so arranged that allowance being made for the
differences of actinism by proportionate exposures there shall be equation in the
action of the light on the plates. This is an important factor because to obtain
bigh excellence in reproductions it is essential that the negatives should corre-
spond in evenness. Although the 3 negatives will naturally show differences of
opacity and transparency according to the part the particular primary color plays
in the composition of the coloring of the object photographed, yet the images
must balance in force and value, i.e. the lights and shadows must show the same
density and intensity and there must be correctness in contrasts and equivalence
in the gradations from the light to the dark tints. In practice the attainment
of these requisites has offered great difficulties more especially as regards the
green and red plates and though the disturbing effect of unequal negatives is
not so apparent in a purely photographic positive, it is strongly evident in the
production of mechanical printing blocks.
The so called ordinary gelatine plate being perfectly adapted for exposure to
the blue rays it is only the other two plates that require suitable preparation.
For exposure to the green rays I employ a gelatine plate which I sensitise
for green by immersion in a bath consisting of a solution of a red coloring sub-
stance for instance the well known erythrosin. But the solution must be so
proportioned that apart from mere color sensitiveness the plate should both by
itself and in relation to the other plates yield the equality above described.
To this end and without prejudicing sensitiveness there should be sufficient
resistance to the property of green rays to abundantly penetrate a silver plate
so that a correct ratio between penetration and the formation of the image may
be established. Taking for instance erythrosin I use a solution of 0,005%
water but other sensitisers may be substituted provided they fulfil the same
conditions.
The plate to be exposed behind the red filter needs to be sensitised with a
combination of a red and blue coloring substance although either is by itself

page_text: sensitive to the red rays. If a red sensitiser only were used most of the red
rays would be reflected without being absorbed thus the formation of a proper
image would be prevented; on the other hand the blue sensitiser alone would
be far more sensitive to the purely red rays than to the orange so that incorrect
contrasts and values would result; moreover it presents no obstacle to the pro-
perty possessed also by red rays of penetrating abundantly a silver plate. By
combining the two sensitisers and moreover in such a manner that their defects
are rendered inactive which best results if the blue sensitiser be superimposed
on the red a balance is created which not only ensures the absorption of the
total rays within the group but establishes the necessary ratio between rate of
absorption and formation of image.
To achieve my object I use as a sensitising bath for instance a solution of
say 0002 cyanin blue and erythrosin in a fluid composed of 60 % water
and 40% alcohol. By this means the red dye which is more soluble in the
water is carried into the film while the blue dye which is more soluble in
alcohol remains substantially in the surface of the plate. But other sensitisers
having the same properties or result may be used.
It will be seen from the aforesaid that apart from the sensitising of the plates
individually my principal object is to obtain the proper adjustment of the
3 negatives to each other and it is obvious that other methods of sensitising
than those described may be used so long as the same necessary adjustment is
achieved.
Owing to the differences in actinism each of the plates requires as already
mentioned a different length of exposure.
Nevertheless by observances of the method of sensitising herein described the
reduction of the time necessary for exposure of the " green "and the "red"
plates can be very greatly reduced below that formerly necessary. Given an
indentical light, electric light for instance, there is no trouble in observing
the necessary proportions but in day light this is frequently very difficult.
I assure exact proportionate exposures irrespective of variations in light by
timing the exposure according to the gyration of a radiometer (light propelled
mill) which revolves faster or slower according to the intensity of the light
playing on it.
Dated this 15th day of June 1899.
HERBERT HADDAN & Co.,
Agents to Applicant.
Improvements relating to the Sensitizing and Relative Sensitive
Adjustment of Photographic Plates or the like for use in Color
Photography and to the Measurement of Time Exposure of said
Plates.
I. GUSTAV SELLE, of Brandenburg, in the Empire of Germany, Physician,
do hereby declare the nature of this invention and in what manner the same is
to be performed to be particularly described and ascertained in and by the
following statement:-
In three color photography the sensitive plates for the three necessary nega-
tives must be constituted so that each shall be preponderatingly sensitive to the
light rays passing through the particular light filter behind which it is exposed,
the ordinary monochromatic silver plate being extremely sensitive to the rays

page_text: contained in the spectral section F to H requires no special treatment: on the
other hand the plates for the green and the red rays must be color sensitized,
i.e. must be rendered particularly sensitive to those rays respectively. Further
the color sensitiveness must be so arranged that allowance being made for the
differences of actinism by proportionate exposures there shall be equation in the
action of the light on the plates. This is an important factor because to obtain
high excellence in reproductions it is essential that the negatives shall corre
spond in evenness. Although the three negatives will naturally show differences
of opacity and transparency according to the part the particular primary color
plays in the composition of the coloring of the object photographed, yet the
images must balance in force and value, i.e. the lights and shadows must show
the same density and intensity and there must be correctness in contrasts and
equivalence in the gradations from the light to the dark tints. In practice the
attainment of these requisites has offered great difficulties more especially as
regards the green and red plates and although the disturbing effect of unequal
negatives is not so apparent in a purely photographic positive, it is strongly
evident in the production of mechanical printing blocks.
The so-called ordinary gelatine plate being perfectly adapted for exposures to
the blue rays it is only the other two plates that require suitable preparation.
For exposure to the green rays I employ a gelatine plate which I sensitize
for green by immersion in bath consisting of a solution of a red coloring sub-
stance for instance the well known erythrosin. But the solution must be so
proportioned that apart from more color sensitiveness the plate should both by
itself and in relation to the other plates yield the equality above described.
To this end and without prejudicing sensitiveness there should be sufficient
resistance to the property of green rays to abundantly penetrate a silver plate
so that a correct ratio between penetration and the formation of the image may
be established. Taking for instance erythrosin I use a solution of 0005 per cent.
in water but other sensitizers may be substituted provided they fulfil the same
conditions.
The plate to be exposed behind the red filters needs to be sensitized with a
combination of a red and blue coloring substance although either is by itself
sensitive to the red rays. If a red sensitizer only were used most of the red rays
would be reflected without being absorbed thus the formation of a proper image
would be prevented; on the other hand the blue sensitizer alone would be far
more sensitive to the purely red rays than to the orange so that incorrect con-
trasts and values would result: moreover it presents no obstacle to the property
possessed also by red rays of penetrating abundantly a silver plate. By com
bining the two sensitizers and moreover in such a manner that their defects are
rendered inactive which best results if the blue sensitizer be superimposed on
the red a balance is created which not only ensures the absorption of the total
rays within the group but establishes the necessary ratio between rate of absorp-
tion and formation of image.
To achieve my object I use as a sensitizing bath for instance a solution of say
0.002 per cent. of cyanin blue and erythrosin in a fluid composed of 60% water
and 40% alcohol. By this means the red dye which is more soluble in the
water is carried into the film while the blue dve which is more soluble in alcohol
remains substantially on the surface of the plate. But other sensitizers having
the same properties or result may be used.
It will be seen from the aforesaid that apart from the sensitizing of the plates
individually my principal object is to obtain the proper adjustment of the three
negatives to each other and it is obvious that other methods of sensitizing than
those described may be used so long as the same necessary adjustment is
achieved.
Owing to the difference in actinism each of the plates requires as already
mentioned a different length of exposure. Nevertheless by observance of the
method of sensitizing herein described the reduction of the time necessary for

page_text: وو
exposure of the " green and the "red" plates can be very greatly reduced
below that formerly necessary.
Given an identical light, electric light for instance there is no trouble in
observing the necessary proportions but in daylight this is frequently very
difficult.
I assure exact proportionate exposures irrespective of variations in light by
timing the exposures according to the gyrations of a radiometer (light propelled
mill) which revolves faster or slower according to the intensity of the light
playing on it.
The exposure is directly proportional to the number of revolutions per second
of the radiometer. The first plate exposed is the plate behind the blue filter,
such plate requires hardly more exposure than the ordinary plate in ordinary
monochrome photography and the necessary time for exposure of such plate is
ascertained by means of an actinometer or similar contrivance and the number
of revolutions made by the radiometer having been counted this will constitute
the basis for estimating the number of revolutions necessary for the green and
red plates. Assuming that the exposure of the 3 plates stands as 1 for the blue,
3 for the green, and 18 for the red and that the exposure required for the blue
plate is in accordance with the actinometer, equivalent to 3 revolutions in a
second then the exposure for the green plate will be equivalent to 3 × 3 = 9
revolutions of the radiometer and the exposure for the red plate will be 3 ×
18 54 revolutions.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is: :-
1. In the sensitizing or sensitive adjustment of photographic plates or the
like for particular color rays, sensitizing a plate for the green rays by a solution
of erythrosin proportioned as herein before stated.
2. In the sensitizing or sensitive adjustment of photographic plates or the
like for particular color rays, sensitizing a plate for the red rays by a solution
of cyanin and erythrosin or other equivalent two colored sensitizers proportioned
as herein before stated.
3. In the sensitizing or sensitive adjustment of photographic plates or the
like for particular color rays, sensitizing a plate for the red rays so that the blue
sensitizer may be superimposed on the red sensitizer.
4. In the sensitizing or sensitive adjustment of photographic plates or the like
for particular color rays, sensitizing plates individually and in relation to each
other in such a manner as to obtain the proper adjustment of each other herein
described.
5. In the sensitizing of photographic plates adjusting and proportioning the
color sensitiveness in relation to the light sensitiveness of the silver plate in such
a manner as to obtain the proper ration between light and color absorption herein
described.
6. The method of assuring correct proportionate exposures by means of timing
the three exposures with the gyrations of a radiometer (light propelled mill).
Dated this 12th day of April 1900.
HERBERT HADDAN & Co.,
Agents to Applicant, 18, Buckingham Street, Strand, W.C.