Improvements in the Manufacture of Sensitive Plates and Films for Photographic Purposes.
Year: 1893

page_text: Date of Application, 4th May, 1893
Complete Specification Left, 5th Mar., 1894-Accepted, 28th Apr., 1894
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Sensitive Plates and Films for
Photographic Purposes.
I, CHARLES EDWIN PETTITT of 46 Fleet Street, Torquay, in the County of
Devon, Photographer, do hereby declare the nature of this invention to be as
follows:-
My invention has reference to the manufacture of sensitive plates and films for
photographic purposes and its object is to prevent or diminish halation (local over-
exposure) and solarization (reversal of the image).
With this object I interpose between the sensitive emulsion and the glass plate
or other support a colored medium which during the exposure in the camera, will
obstruct or entirely absorb the actinic rays of light in their passage to and from
the reflecting surface or surfaces of the glass plate or other support.
In carrying out my invention I coat the plate with a non-sensitive medium or
substratum of gelatine, or albumen or collodion or a similar suitable vehicle, this
medium or substratum being colored or made to contain coloring matter so that it
offers obstruction to the passage of light rays. When the plate thus treated is
thoroughly set and dry, I coat it with an ordinary emulsion of haloid salts of
silver of any required sensitiveness. If thought necessary I isolate the emulsion
from the substratum; this can be effected by applying a thin solution of gum
arabic, albumen or some such suitable substance to the substratum and allowing the
solution to dry before applying the sensitized emulsion.
The colored obstructive medium can be prepared in several ways.
It may for
example be prepared with a harmless dye or pigment of the blues, yellows or reds
of such sufficient density that it is effective to prevent or diminish halation, but
will not unduly interfere with the printing property of the negative; the color may
therefore remain in the finished negative.
Or the color of the medium may be of a distinctly non-actinic character, and be
removed (after exposure in the camera) by the chemical action set up by and
during the subsequent processes of development and fixation. For instance the
medium having been colored red with an acidified solution of litmus, the application
of the ordinary alkaline developer will set up a re-action which will remove the
non-actinic color. Or the medium having been colored with a preparation of
iodine, the color will be removed during the process of fixation by the chemical
bleaching action of the sodium thiosulphate.
The color may also be removed by a chemical treatment before or after
development.
.
1000

page_text: Improvements in the Manufacture of Sensitive Plates and Films for
Photographic Purposes.
I, CHARLES EDWIN PETTITT of 46 Fleet Street, Torquay in the County of
Devon, Photographer, 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 has reference to the manufacture of sensitive plates and films for
photographic purposes and its object is to prevent or diminish halation (local over-
exposure) und solarization (reversal of the image by over-exposure).
With this object I interpose between the sensitive emulsion and the glass plate,
film or other support, a substratum or coating containing a coloring matter which
during the exposure in the camera will entirely absorb or obstruct the actinic rays
of light in their passage to and from the reflecting surface or surfaces of the glass
plate or other support.
In carrying out my invention I coat the plate or film with a non-sensitive
substratum or coating of gelatine, collodion, albumen or other similar suitable
vehicle which has been made non-actinic by the thorough incorporation therewith
of non-actinic coloring matter; the vehicle preferably used for the purpose is
gelatine of the same physical character as that employed in the preparation of the
sensitive emulsion used on the plate or film. When the non-actinic, non-sensitive
substratum has become thoroughly set and dry I coat it with an ordinary emulsion
of haloid salts of silver of any required sensitiveness.
The emulsion can if thought desirable be isolated from the substratum by
applying to the substratum when dry a thin solution of gum arabic or. albumen
which is allowed to dry before the emulsion is applied, but in practice I have not
found this isolation necessary.
The colors which I prefer to employ for coloring the substratum so as to render
it non-actinic are the compounds of carbon and hydrogen, or of carbon, hydrogen
and oxygen, or of carbon, hydrogen and nitrogen, commonly known as derivatives
of naphthaline, phenol, aniline and toluidine.
These coloring matters are of such a nature that they disappear during the
subsequent manipulations of development, fixation and washing of the negative, they
are readily dissociated by the chemical reaction set up by the developer, and they
are besides freely soluble in the developer, in the fixing bath and in the washing
water. They therefore disappear, and the resulting negative is of the usual quality
and color.
In case a very tenacious gelatine is employed for the substratum it is sometimes
necessary to somewhat prolong the washing process so as to ensure that the color is
removed.
The interposition in accordance with my invention of a non-actinic colored
substratum or coating between the sensitive emulsion and the glass or other support
effects two specific results, viz. :—
1st. During the necessary. exposure of the sensitive plate or film to light, the
non-actinic substratum prevents reflective halation by obstructing the actinic rays
of light in their passage to and from the glass plate or other support.
2nd. All reflected light which is returned into the plate or film is rendered non-
actinic by its passage through the non-actinic substratum, and therefore solarization
is diminished or prevented, because the further free action of light during exposure
is retarded in direct proportion to its actinic energy.

page_text: 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 :-
In a sensitive plate or film for photographic purposes, a non-actinic, non-sensitive
substratum or coating between the sensitive emulsion and the glass plate or other
support for the purpose hereinbefore described, the said substratum being colored
with non-actinic color that disappears after the exposure during the manipulations
of development, fixation and washing, or owing to chemical action set up during
development, as set forth.
Dated this 5th day of March 1894
J. C. MEWBURN,
55 & 56, Chancery Lane, London, Chartered Patent Agent.