Improvements in the Manufacture and Production of Emulsions and other Materials Sensitive to Light.
Year: 1890

page_text: Date of Application, 19th June, 1890
Complete Specification Left, 7th Mar., 1891-Accepted, 11th Apr., 1891
PROVISIONAL SPECIFICATION,
Improvements in the Manufacture and Production of Emulsions and
other Materials Sensitive to Light.
I, WASSILY REBIKOW, Honorary Hereditary Citizen of Alechki, Tambow
Government, in the Empire of Russia, do hereby declare the nature of this invention
to be as follows:
:-
"'
In the preparation of emulsions and the like for photographic purposes according
to my present invention employ the marine alge known as agar-agar as a
substitute for the gelatine and albumen heretofore employed in the preparation of
sensitive emulsions for photographic plates, papers and the like.
I have discovered that agar-agar possesses a valuable property which is that very
weak solutions of this substance (containing even as little as per cent. of agar-agar)
gelatinise rapidly.
L
In pursuing my investigations I have found that the water can be squeezed out
from weak (to 2 per cent.) gelatinised solutions of agar-agar as from a sponge and
in the gelatinous mass of agar-agar which results there may yet remain 8 times as
much water as agar-agar.
In the solutions of the latter very fine particles in suspension are always present
imparting to the liquid a turbid appearance and which cannot be removed by
filtration but I have discovered that by boiling the solution, cooling it to say about
80 degrees Centigrade then reheating it to boiling point and repeating these operations
several times in succession the fine particles held in suspension collect or agglomerate
together in the form of yellowish masses which swim in the now transparent solution.
The compactness of these masses' and the facility with which they form increases in
proportion to the weakness of the solution and the number of successive coolings and
heatings to which it is subjected. The masses also have a tendency to collect in the
hottest parts of the vessel or receptacle containing the solution.
On placing a cylindrical vessel containing the cooled solution of agar-agar (in
which the solid matter has been already agglomerated) in such a manner that the
hot water comes in contact with the lower part only the masses slowly collect
together in this part of the vessel and the clear solution in the upper part can' then
be readily decanted or drawn off by a siphon.
With the same object that is to say effecting the separation of the objectionable
matter from the solution I have devised another method having observed that the
fine particles of matter which cannot be removed even by the most careful filtration
are capable of being attracted by other bodies swimming in the liquid and of
collecting about such bodies. Consequently by introducing pieces of filter paper
(previously soaked in boiling water) or chemically pure cotton (hygroscopic cotton)
or other analogous bodies into the hot solution of agar-agar these substances are
enabled to draw or attract the matter to be removed to the bottom of the vessel so
that the clear solution can be separated therefrom by filtration or decantation.
The solution of agar-agar before it is freed from the matter causing the turbid
appearance cannot be employed with advantage in the preparation of a sensitive
emulsion as the matter favours the formation of fog and also by strongly attracting
bromine and chlorine reduces the bromide of silver into the state of semi bromide
which spoils the emulsion and produces fog.
In order to prepare eniulsions with agar-agar it must be brominated or chlorinated
beforehand without exposure to actinic light being washed in a weak solution of
bromine or chlorine. The brominated or chlorinated agar-agar is afterwards care-
fully washed in pure water in order to remove from it the soluble matters by the

page_text: action of dialysis. To obtain bromide of silver emulsions the agar-agar is preferably
brominated being chlorinated for the chloride of silver emulsions.
After this treatment the solution of agar-agar being purified by filtering through
flannel can be employed in the preparation of sensitive emulsions (chlorinated or
brominated) by any known or ordinary process that is to say by ebullition, by the
ammonia process or by macerating or digesting. In consideration of the difficulties
attending the employment of very dense or pasty emulsions (such as a 10 per cent.
solution for example) it is preferable to employ solutions containing not more than
2 per cent. of agar-agar the solutions being of a syrupy consistency even at this
degree of concentration.
If the process by ebullition be preferred it is advantageous to employ a liquid
emulsion containing a large quantity of bromine. In the ammonia process the best
results are obtained by employing more or less dense emulsions containing a large
quantity of silver.
The advantages arising from the employment of agar-agar in the preparation of
sensitive emulsions are numerous.
For instance it is possible to obtain a far higher degree of sensitiveness with agar-
agar than is possible with gelatine the agar-agar being much better adapted than
gelatine to resist the destructive action of ammonia and heat. Moreover the agar-
agar tends to spontaneously increase its sensitiveness as in order to obtain the same
degree of sensitiveness with the same method of treatment and the same formula
the gelatine emulsion has to be boiled for at least half an hour whereas 8 minutes
are quite sufficient for the agar-agar. The plates and papers are enabled to be
washed and dried with great case and rapidity owing to the permeability of the
coating and its capacity for withstanding an elevated temperature.
Owing to the rapidity and the elevated temperature with which the agar-agar
solution becomes gelatinised (35 to 40 degrees Centigrade according to the degree
of concentration) the emulsions are enabled to be prepared during hot weather or in
hot climates.
Agar-agar in the form of an emulsion is capable of taking up a great quantity as
much as 5 times its weight of silver and its price is very low.
Photographic paper coated with a chlorinated agar-agar emulsion can be worked
upon with colours or pencils without any preparation even after it has been
burnished and can be caused to acquire a brilliant enamelled appearance by drying
upon a glass plate.
Owing to the permeability of the coating less time than usual is required for
the operations of washing fixing toning and the like and weaker solutions are
enabled to be employed..
The coating of agar-agar does not run when acted on by warm solutions.
I find moreover that by placing a dry coating or layer of agar-agar containing a
chloride in contact with a solution of nitrate of silver chloride of silver in an
extremely fine state of division is almost instantaneously formed in the coating
owing to its permeability. This property enables the agar-agar to be employed in
place of albumen in the preparation of photographic papers.
The solution of nitrate of silver for the silver bath does not require to be so
strong as when albumen is employed.
The agar-agar acting as a sensitising agent in itself the sensitiveness of plates,
films, paper and the like prepared with agar-agar is much greater than when
albumen or the like is employed the cost is less and at the same time the various
operations to which the plates paper or the like have to be subjected are greatly
facilitated as herein before explained.
Dated this 19th day of June 1890.
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C., Agents.

page_text: COMPLETE SPECIFICATION.
Improvements in the Manufacture and Production of Emulsions and
other Materials Sensitive to Light.
1, WASSILY REBIKOW, Honorary Hereditary Citizen, residing at Alechki,
Tambow Government, in the Empire of Russia, 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 :-
My invention relates to the manufacture and production of emulsions and other
materials sensitive to light employed in the manufacture of plates, films papers or
other sensitive surfaces employed in photography and it consists essentially in the
employment as hereinafter described of the marine algae known as agar-agar in place
of the gelatines and albumens which have heretofore been usually employed in the
manufacture of these emulsions.
Attempts have been made to employ agar-agar for these purposes but they have
not been productive of any useful result. I have now discovered that agar-agar
possesses certain peculiar properties and have availed myself of this discovery to
overcome the difficulties which stood in the way of its employment for photo-
graphic purposes. Weak solutions of agar-agar gelatinise rapidly even when they
do not contain more than about per cent. of agar-agar and I find that the water
can be squeezed out of a weak gelatinised solution (to 2 per cent. for example) as
from a sponge and in the gelatinous mass of agar-agar which results there may yet
remain 8 times as much water as agar-agar.
In the solutions of the latter very fine particles in suspension are always present
imparting to the liquid a turbid appearance and which cannot be removed by
filtration but I find that by boiling the solution, cooling it to say about 80 degrees
Centigrade, then reheating it to boiling point and repeating these operations
several times in succession the fine particles held in suspension collect or agglomerate
together in the form of yellowish masses which swim in the now transparent
solution. The compactness of these masses and the facility with which they form
increases in proportion to the weakness of the solution and the number of successive
coolings and heatings to which it is subjected. The masses also have a tendency
to collect in the hottest parts of the vessel or receptacle containing the solution.
On placing a cylindrical vessel containing the cooled solution of agar-agar (in
which the solid matter has been already agglomerated) in such a manner that the
hot water comes in contact with the lower part only or extends to say about of
the height of the cylinder for example the masses slowly collect together in this
part of the vessel and the clear solution in the upper part can then be readily
decanted or drawn off by a siphon.
With the same object that is to say effecting the separation of the objectionable
matter from the solution 1 have devised another method having observed that the
fine particles of matter which cannot be removed even by the most careful filtration
are capable of being attracted by indifferent or neutral bodies swimming in the
liquid and of collecting about such bodies. Consequently by introducing pieces of
filter paper (previously soaked in boiling water) or chemically pure cotton (hygro-
scopic cotton) or other analogous bodies into a hot solution of agar-agar, these
substances are enabled to draw or attract the matter to be removed to the bottom
of the vessel so that the solution is clarified and can be removed by filtration or
lecantation.
The solution of agar-agar before it is freed from the matter causing the turbid
appearance cannot be employed with advantage in the preparation of a sensitive
emulsion as the said matter favours the formation of fog and also by strongly
ttracting bromine and chlorine reduces the bromide of silver into the state of
semi-bromide which spoils the emulsion and produces fog.
In order to prepare. emulsions with agar-agar it must be brominated or
chlorinated beforehand without exposure to actinic light being washed in a weak

page_text: solution of bromine or chlorine. The brominated or chlorinated agar-agar is after-
wards carefully washed in pure water in order to remove from it the soluble matters
by the action of dialysis. To obtain bromide of silver emulsions the agar-agar
is preferably brominated being chlorinated for the chloride of silver emulsions.
After this treatment the solution of agar-agar being purified by filtering through
flannel can be employed in the preparation of sensitive emulsions (chlorinated or
brominated) by any known or ordinary process that is to say by ebullition, by the
ammonia process or by macerating or digesting. In consideration of the difficulties
attending the employment of very dense or pasty emulsions (such as a 10 per cent.
solution for example) it is preferable to employ solutions containing not more than
2 per cent, of agar-agar the solutions being of a syrupy consistency even at this
degree of concentration.
If the process by ebullition be preferred it is advantageous to employ a liquid
emulsion containing a large quantity of bromine. In the ammonia process the best
results are obtained by employing more or less dense emulsions containing a large
quantity of silver.
The advantages arising from the employment of agar-agar in the preparation of
sensitive emulsions are numerous. For instance it is possible to obtain a far higher
degree of sensitiveness with agar-agar than is possible with gelatine the agar-agar
being much better adapted than gelatine to resist the destructive action of ammonia
and heat. Moreover the agar-agar appears to spontaneously increase the sensitive-
ness as in order to obtain the same degree of sensitiveness with the same method
of treatment and the same formula the gelatine emulsion has to be boiled for at
least half an hour whereas 8 minutes are quite sufficient for the agar-agar.
The plates and papers or the like are enabled to be washed and dried with great
case and rapidity owing to the permeability of the coating and its capacity for
withstanding an elevated temperature agar-agar being fusible at from 90 to 100
degrees Centigrade according to the density of the solution.
The gelatinised solution not only admits of being readily impregnated with
water but also allows of the water being readily expressed or extracted in order to
obtain any desired degree of concentration. Owing to the rapidity and the elevated
temperature with which the agar-agar solution becomes gelatinised (35 to 40
degrees Centigrade according to the degree of concentration) the emulsions are
enabled to be prepared during hot weather or in hot climates. Agar-agar_in_the
form of an emulsion is capable of taking up a great quantity or as much as 5 times
its weight of silver and can be obtained at a relatively low price.
Paper prepared with agar-agar and chloride of silver is more sensitive than
gelatinised paper prepared in the same way. The coating of agar-agar does not
run when acted on by heated solutions.
'I find moreover that by placing a dry coating or layer of agar-agar containing
a chloride in contact with a solution of nitrate of silver chloride of silver in an
extremely fine state of division is almost instantaneously formed in the coating
owing to its permeability. This property enables the agar-agar to be employed in
place of albumen in the preparation of papers for positive images.
In the silver bath the solution of nitrate of silver may be comparatively weak
the coating of agar-agar being insoluble whereas with albuminised paper it is
necessary to employ a bath containing from 8 to 10 per cent. of nitrate of silver in
order to ensure the coagulation of the albumen that is to say in order to render it
insoluble. By thus employing weaker baths a considerable economy is effected.
For toning weaker solutions of gold may be employed in like manner owing to the
same property (permeability) of agar-agar thus likewise effecting a considerable
economy considering the high price of salts of gold.
The agar-agar acting as a sensitising agent in itself the sensitiveness of plates
films paper and the like prepared with agar-agar is much greater than when
albumen or the like is employed the cost is less and at the same time the various
operations to which the plates papers or the like have to be subjected are greatly
facilitated as hereinbefore explained.

page_text: The coating of agar-agar admits of being burnished with the same facility as
albumenised paper. Paper prints prepared with agar-agar can be easily worked
upon with colours or pencil even after it has been burnished this being practically
impossible with albumenised paper.
1
By drying upon a glass plate the coating of agar-agar acquires the polish and
brilliancy of an enamelled surface which cannot be produced in this way with
albumenised paper.
The operation of coating the paper is greatly facilitated by the employment of
agar-agar and the coated paper can be quickly dried by exposure to a temperature
of from 80 to 85 degrees Centigrade thus reducing the cost of manufacture of the
paper for photographic printing.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is-
1. The employment of agar-agar in the manufacture of emulsions or materials
for photographic purposes the solution of the said agar-agar being purified or
clarified by the extraction of the matter producing the turbid appearance in the
solution substantially as hereinbefore described.
2. Clarifying an aqueous solution of agar agar by repeated heatings and coolings
or by mechanically attracting the matter to be removed by means of a neutral or
indifferent substance substantially as and for the purpose herein before described.
3. The improvements in the manufacture and production of emulsions and other
materials sensitive to light substantially as hereinbefore described.
Dated this 7th day of March 1891
J. H. JOHNSON & Co.,
47, Lincoln's Inn Fields, London, W.C., Agents.