An Improved Method of Deciding the Correct Exposure in Platinotype Printing and Apparatus therefor.
Year: 1889

page_text: Date of Application, 28th June, 1889
Complete Specification Left, 12th Mar., 1890-Accepted, 19th Apr.. 1890
PROVISIONAL SPECIFICATION.
An Improved Method of Deciding the Correct Exposure in
Platinotype Printing and Apparatus therefor.
1 CHARLES ROBERT CRAWFORD of 40 Monmouth Road Bayswater in the county of
Middlesex Gentleman do hereby declare the nature of this invention to be as
follows:-
In platinotype printing that is to say in printing off numerous prints from a
negative on platinotype paper a great difficulty is experienced in deciding what
amount or length of exposure in the printing frame is correct whereby very often
prints are spoiled and the platinotype paper wasted. Now the object of my invention
is to provide a method of deciding the correct exposure in platinotype printing and
apparatus for use in the same by which this difficulty will be materially if not entirely
obviated and destroyed.
To carry out this object I take a negative of a number or series of letters or
figures or signs and when this negative has been duly developed and properly treated
for printing I cover the first letter or figure or sign with one layer of fine tracing
paper or other suitable material and the second letter or figure or sign with two
layers of paper or material and the third letter or figure or sign with three layers of
paper or material and so on providing as many letters or figures or signs as may be
desired and covering the same if necessary with glass and under this negative so
treated 1 place a piece of ordinary sensitized paper enclosing the whole in a suitable
printing frame. In the same frame or in another by its side I place the platinotype
paper under its negative which has also been properly treated and I give these two
prints the same exposure until the platinotype print has been correctly exposed when
1 note the letter or figure or sign that is just visible in the first mentioned or
deciding print. The next prints are arranged for and from both the negatives in
the same way and when the letter or figure or sign noted as above is again just visible
in the deciding print the correct exposure has again been given to the platinotype
print and in this manner all these platinotype prints will be exactly alike when they
are finished off in the usual manner care being taken that the bath is kept at about
the same temperature.
When the trial exposure has not been quite exactly correct it will be easy to
make a due allowance therefor and note a letter or figure or sign before or behind
that which is just visible as aforesaid.
Dated this 28th day of June 1880
COMPLETE SPECIFICATION.
An Improved Method of Deciding the Correct Exposure in
Platinotype Printing and Apparatus therefor.
I CHARLES ROBERT CRAWFORD of 40 Monmouth Road Bayswater in the county of
Middlesex Gentleman 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 platinotype printing that is to say in printing off from a negative numerous
prints on platinotype paper a great difficulty is frequently or even constantly
experienced in deciding what amount or length of exposure in the printing frame
is correct and produces the desired result whereby very often prints are spoiled and
the platinotype paper wasted.
Now the object of this my invention is to provide a method of deciding the

page_text: correct exposure in platinotype printing and apparatus for use in the same by which
this difficulty aforesaid will be materially if not entirely obviated and destroyed and
the desired result the more surely produced.
To carry out this object I take in any usual and convenient manner a negative
of a number or series of letters or figures or signs of any description arranged in
such a consecutive or other manner horizontally or vertically or otherwise as may be
desired in each particular case and when this negative has been duly developed
and otherwise properly treated in the usual or other manner for printing I cover
the first er one letter or figure or sign with one layer or thickness of fine tracing
paper or other suitable and semi-transparent or semi-translucent material and the
second or another letter or figure or sign with two layers or thicknesses of similar
paper or material and the third or another letter or figure or sign with three layers
or thicknesses of similar paper or material and so on providing as many different
letters or figures or signs and therefore as many different thicknesses of the paper or
material as may be desired or may be necessary and the whole can very conveniently
be covered with glass whereon I should place some perfectly opaque paper or other
suitable material in such position as to cover and prevent any access of light to that
part of the negative if any on which the letters or figures or signs aforesaid are not.
Under this negative so treated and fitted and arranged as herein before described
I place a piece of any usual and ordinary sensitized paper or material and I can if
desired conveniently enclose the whole that is to say the negative and the paper or
material in any usual and suitable printing frame and I preferably arrange and form a
suitable scale and apply the same to the negative either on the edges thereof or
elsewhere thereon or on the printing frame if any or otherwise the marks on which
scale can conveniently correspond with or have reference to the several letters or
figures or signs aforesaid whereby the correct and exact placing and replacing of the
sonsitized paper or material under the negative will be facilitated and the danger of
and consequent waste from the erroneous placing and replacing of the same thore
under will be eliminated.
The negative from which the platinotype prints are to be produced is likewise
duly developed and otherwise properly treated in the usual or other manner for
printing and the platinotype paper is placed thereunder the whole likewise if desired
being enclosed in the same or in another printing frame.
I then give these two prints aforesaid that is to say the first before mentioned
or ordinary print and the platinotype print an exposure of the same duration until
the platinotype print has been correctly exposed or until I consider such to be the
case when I note the letter or the figure or the sign that is just visible in the first
before mentioned or ordinary print which print is thus constituted by this particular
letter or figure or sign and in future will act as the deciding print.
When this trial exposure has been proved on and by the finishing off in the
usual manner of the platinotype print to be not exactly correct it is obvious that
it will be easy to make a due allowance therefor and note a letter or a figure or
a sign before or behind that which is just visible as aforesaid in the deciding print
according as a shorter or a longer exposure is required and thus so long as the trial
will not be wasted but will afford the desired
exposure is approximately correct
information.
The next prints that is to say both the first before mentioned or ordinary print
and the platinotype print are arranged for and with and are produced from both these
-aforesaid negatives in the same way and when the particular letter or figure or sign
so noted as herein before described is again just visible in the deciding print the
correct exposure has again been given to the platinotype print and in this manner
all these platinotype prints will receive the correct exposure and will be exactly alike
when they are finished off in the usual manner care being taken that the bath is kep
at about the same temperature.
As is hereinbefore stated I preferably use different letters or figures or signs or
and in the first before mentioned negative for such use will obviously facilitate the
remembrance of the particular letter or figure or sign to be noted as aforesaid in
"

page_text: the deciding print but I do not limit myself thereto for any letters or figures or signs
of any description may be used.
As also is herein before stated I preferably cover the several letters or figures
or signs on and in the first before mentioned negative with fine paper or material in one
and in two and more layers or thicknesses for this arrangement and method is not
only the easiest and quickest in formation and construction but also is the surest and
most regular in the graduation of the required and necessary absorption or inter-
ception of the light but neither do I limit myself thereto for separate pieces of
paper or material of different thicknesses or of varying degrees of semi-transparency
or semi-translucency or powers of absorption or interception of the light may be used
to cover the several letters or figures or signs.
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
The method of and apparatus for deciding the correct exposure in platinotype
printing substantially as hereinbefore described and set forth.
Dated this 12th day of March 1890.