Plates Highly Sensitive to Light.
Year: 1886

page_text: Plates Highly Sensitive to Light.
I, Dr. HERMANN WILHELM VOGEL of No. 124 Kurfürsten Strasse in the City of
Berlin, Prussia, Germany, Chemist, do hereby declare the nature of my Invention for
"AN IMPROVED PROCESS FOR MANUFACTURING ISOCHROMATIC EMULSION PLATES
HIGHLY SENSITIVE TO LIGHT" and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement :-
My invention relates to an improved process for manufacturing isochromatic
gelatine and emulsion and gelatine plates for photographic purposes and to chemical
preparations requisite for such said process.
In the year 1873, I made the discovery that chloride and bromide of silver, which
are only sensitive to violet, indigo and the blue light of the spectrum, can be made
sensitive to green, yellow and red rays by mixing the above-mentioned salts with
bodies which absorb the latter rays.
If, for instance, chloride or bromide of silver is mixed with aniline red, which
absorbs yellow rays, the chloride or bromide will become sensitive to yellow rays; or
if chloride or bromide of silver is mixed with aniline green, which absorbs red rays,
the same will be made sensitive to red rays.
I denominated these bodies, which sensitize silver salt in the aforesaid manner,
optical sensitizers, and I and others after me have discovered a large number of such
optical sensitizers amongst the dyes, and in this manner the so-called isochromatic
gelatine plates, colored with an optical sensitizer such as cyanine, chinoline red, cosine,
erythrosine are now articles of commerce.
All these isochromatic gelatine plates are generally less sensitive than ordinary
plates and require a yellow glass plate interposed between the lense and the sensitive
plate for diminishing the power of the blue light.
By this interposition of a yellow plate the time of exposure was lengthened and if
the surface of the plate was not quite even, the sharpness of the photograph was lost,
so that these isochromatic plates are used on a small scale only for the reproduction of
pictures or paintings, but not for portrait or landscape photography.

page_text: Now I have succeeded in making isochromatic gelatine plates, the sensitiveness of
which is twice as great as that of the ordinary gelatine plates and which do not
require any yellow plate or screen.
This discovery is based.
1,on the application of the eosides of silver, that is, the chemical combinations of
cosine dyes with silver. These eosine dyes or derivatives of fluoresceine are all acids
and combine with silver to salts.
2, on the addition of silver salts to other optical sensitizers, for increasing their
sensitizing power.
As early as 1884, I observed this favorable influence of the presence of silver salts
and proved, for instance, that eoside of silver will give ten times more sensitiveness
for yellow light, than ordinary cosine, but I have only now succeeded in making
plates without fog or film and spots, so that I can introduce the process into practice
and I have proved that it is possible to produce in this manner, landscapes and
portraits, far superior to those taken with ordinary plates.
I have now invented the following methods for making highly sensitive isochromatic
plates or sensitizing solutions, so that any photographer or amateur can prepare his
own isochromatic plates.
In order to attain this object I proceed as follows:-
1. Ordinary gelatine plates are bathed in a solution of a soluble salt of silver
(11000), then in a solution of an eosine dye, or a mixture of cosine dyes, or a mixture
of an eosine dye with other optical sensitizers, with or without liquor of ammonia.
The solution of the dye can also be used first and the silver solution afterwards, or an
emulsion can be mixed with a soluble salt of silver and the dye added to the mixture,
or vice versa, and with or without ammonia.
2. A silver eoside is formed by mixing a solution of an eosine dye or a mixture of
different eosine dyes (for instance, ordinary cosine, blue tinted cosine, chrysoline,
aureosine, phloxine, Bengal rose or any other derivative of fluorescine), with a soluble
salt of silver, such as sulphate, nitrate, acetate or fluoride of silver.
This coside of silver can be collected as a precipitate, washed and mixed with the
emulsion, or dissolved in diluted ammonia or diluted acetic acid and employed as a
bath for soaking dry plates, but I prefer to add liquid ammonia, carbonate of ammonia
or acetic acid, during the process of precipitation, so that the suspended precipitate is
dissolved and to employ the same as sensitizing agent for fluid emulsions, or the said
solution can be diluted with water and used as a bath for dry plates. The quantity of
this solution of eoside of silver, to be employed, varies according to the quality and
kind of emulsion treated with the same, although the following formula will serve as a
general guide for those employing my sensitizing solution―
50 Cubic Centimeters of a solution of an cosine dye,
(1 part dye to 1000 parts water or dilutod alchol),
1 Cubic Centimeter of a solution of nitrate of silver,
(1 part nitrate of silver to 20 parts of water),
1 to 2 Cubic Centimeters of liquor of ammonia.
This solution is either mixed with the emulsion, that is, 5 to 10 per cent is added to
the emulsion, or the same is diluted with 200 to 500 cubic centimeters water and the
gelating plates immersed or soaked in the same for about one minute and then dried.
3. I furthermore use other dyes, known as optical sensitizers, which do not
chemically combine with silver, but the sensitiveness of which is much improved by
the presence of a soluble salt of silver such, for instance, as cyanine, chinoline red,
coruleine etc, and mix them with any soluble salt of silver. I employ, for instance,
50 Cubic Centimeters chinoline red, or a mixture of chinoline red and cyanine
(solution 1 1000)
1,5 to 3 cubic centimeters nitrate of silver (solution, 1 : 20),
15 cubic centimeters, ammonia liquor.
This solution is emploved in the same manner as the eoside of silver solution

page_text: I furthermore, employ the solutions described under 2 and 3, in varying proportion
for improving the sensitiveness for any part of the chromatic spectrum.
4.I likewise employ, in like manner as mentioned under 1, 2, 3, the salts of lead
which produce, when mixed with an eosine dye, eoside of lead, which said salts can be
employed alone or mixed with eoside of silver.
I furthermore, employ the insoluble salts of silver, such as the chlorides, tartrates,
citrates etc, dissolved in ammonia or acid.
I do not confine myself to any of the proportions of the mixtures as given in the
foregoing specification, as the same can be varied according to requirement, without
in any way departing from the nature of my invention.
Having now particularly described and ascertained the nature of my said Invention,
and in what manner the same is to be performed, I declare that what I claim is :-
:-
1. The application and employment of the chemical combinations of silver or
lead, with an cosine dyo or cosine dyes, for producing highly sensitive isochromatic
emulsion or gelatine plates, substantially as and for the purpose set forth in the
foregoing specification.
2. The application and employment of dyes, known as optical sensitizers, in
combination with the salts of silver, substantially as and for the purpose set forth
in the foregoing specification.
3. The application and employment of various dyes, as mentioned in claims
1 and 2, in combination with soluble salts of silver, substantially as and for the
purpose set forth in the foregoing specification.
4. The manufacture of combinations or solutions of dyes and silver, as strong
optical sensitizers for coloring gelatine emulsions, or as bath for gelatine plates,
substantially as and for the purpose set forth in the foregoing specification.
5. The application of silver salts not soluble in water, but in ammonia or acid,
substantially as and for the purpose set forth in the foregoing specification.
LISON BROS.,
Agents for the Applicant.