Method and Apparatus for Timing Photographic Development.
Year: 1893

page_text: Date of Application, 12th Dec., 1893
Complete Specification Left, 31st Aug., 1894-Accepted, 6th Oct., 1894
PROVISIONAL SPECIFICATION.
Method and Apparatus for Timing Photographic Development.
I, ALFRED WATKINS, of The Imperial Flour Mills, Hereford, Master Miller,
lo hereby declare the nature of this invention to be as follows :-
11
In photographic development considerable experience is required for estimating
correctly how long the plate should be left in the developer, as the appearance of
the plate is not much guide in the matter. The length of time necessary varies
with the amount of alkali and restrainer in the developer, and also with the
temperature thereof.
I have ascertained by numerous experiments that the total length of time of
development required to bring a correctly exposed plate to a given density is
always a definite multiple of the time which elapses between the pouring on of the
developer and the first appearance of the image. I have found that this multiple
is always the same for a particular make of plate, but varies with different makes.
If therefore the time between the pouring on of the developer and the appearance
of the image be determined, which observation is easily made, this time forms a
reliable basis to determine the total time required for leaving the plate in the
developer.
According to my present invention I determine this time by means of an instru-
ment so arranged that on setting an indicator in action when the developer is
poured on, and on effecting a change in such action when the image appears, the
continued modified action of the indicator will correctly automatically indicate the
desired multiple of the first obtained indication. Such instrument may be variously
constructed for carrying out this mode of action. Thus according to the simplest
construction which I prefer to employ, I construct a glass vessel somewhat similar
to an ordinary sand hour glass, so arranged that when turned up one way, the sand
runs through at a speed from four to ten times faster (regulated by adjustment)
than when standing the other way up.
If therefore the sand is started to run at the faster rate at the moment when the
developer is poured on the plate, and the instrument is turned upside down when
the image appears, the quantity of sand which had run through has now to run
back at the slower rate, so that, assuming that the instrument has in the first
instance been adjusted, to the correct multiple for the particular make of plate,
then by the time the whole of the sand has run back, the plate will be found to
have been correctly developed.
The construction of the instrument which I prefer to employ is as follows:
A glass tube is formed with a restricted passage near one end, the orifice of which
passage has projecting into it the point of a stem screwing through the end cover
of the tube, so that by turning the stem in one direction or the other, the stem is
advanced or withdrawn so as to either reduce or enlarge the size of the opening.
The outer end of the screw stem is provided with a pointer which points to a
circular scale on the cover, indicating the positions into which the stem has to be
turned for a certain make of plate. Within the other part of the tube is fixed
concentrically a second tube closed at one end all but a very small orifice, which is
presented opposite the restriction of the outer tube, while the other end of the
inner tube is wide open.
"
The outer tube extends beyond this end of the inner.tube and is formed beyond
the same with a moderate restriction. The part of the outer tube terminating
in the adjustable orifice, being charged with sand, then on turning this part of the
instrument uppermost the sand will flow through the adjustable orifice and through

page_text: the annular space between the inner and outer tubes into the space at the other end
of the outer tube. If on the appearance of the image as before stated, the instru
ment be reversed then the sand which had run into the other end of the tube will
now be caused by the before mentioned restriction, to run into the interior of the
inner glass, from which it will now run at a much slower rate through the small
opening back into the first named end of the outer glass, so that by the time the
sand has run back entirely the development will be completed.
It will be obvious that the same or a similar instrument might be made to work
with a liquid instead of sand, also, that air or other gaseous fluid might be forced
to flow first through a hole or holes of a certain size, and then the same volume of
air be forced to flow through a smaller hole or holes.
Again, a clockwork movement may be used in which a certain part is made to
travel a certain distance until the image appears and then has its action so modified
that after the expiration of the required multiple of that time it will give a visible
or audible indication of the termination of such time.
Dated this 12th day of December 1893.
ABEL & IMRAY,
Agents for the Applicant.
Method and Apparatus for Timing Photographic Development.
I, ALFRED WATKINS, of The Imperial Flour Mills, Hereford, Master Miller,
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 photographic development considerable experience is required for estimating
correctly how long the plate should be left in the developer, as the appearance of
the plate is not much guide in the matter. The length of time necessary varies
with the amount of alkali and restrainer in the developer, and also with the
temperature thereof.
I have ascertained by numerous experiments that the total length of time of
development required to bring a correctly exposed plate to a given density is
generally a definite multiple of the time which elapses between the pouring on of
the developer and the first appearance of the image. I have found that this
multiplying factor is always the same for a particular make of plate, but varies
slightly with different makes; the multiplying factor also varies with different
kinds of developers. If therefore the time between the pouring on of the developer
'and the appearance of the image be determined, which observation is easily made,
this time forms a reliable basis to determine the total tine required for leaving the
plate in a particular developer, as it makes correct allowance for variations in
temperature, or in amount of bromide or alkali.
The above described method of operating may be carried out by means of
variously arranged instruments, thus an instrument may be so constructed that on
setting an indicator in action when the developer is poured on, and on effecting a
change in such action when the image appears, the continued modified action of
the indicator will correctly automatically indicate the desired multiple of the first
obtained indication.
An instrument operating in this manner is shewn in vertical section at Fig. 1 of
the accompanying drawing.
A glass tube A is formed with a restricted passage at A' near one end, the orifice
of which passage has projecting into it the point of a stem B screwing through
the end cover C of the tube, so that by turning the stem in one direction or the
other, the stem is advanced or withdrawn so as to either reduce or enlarge the
size of the opening. The outer end of the screw stem is provided with a pointer D

page_text: which points to a circular scale marked on the cover C, indicating the
nto which the stem has to be turned for a certain developer. Within the other
part of the tube is suitably fixed in a concentrical position a second tube E closed
at one end all but a very small orifice E' which is presented opposite the restriction
of the outer tube A, while the other end of the inner tube is wide open. The
outer tube A extends beyond this end of the inner tube and is formed beyond the
same with a moderate restriction A'. The part As of the tube terminating in
the adjustable orifice A', being charged with sand, then on turning this part of
the instrument uppermost the sand will flow through the orifice A¹ and through the
annular space F between the inner and outer tubes into the space A' at the other
end of the tube A. If, on the appearance of the image as before stated, the
instrument be reversed then the sand which had run into A³ will now be caused by
the restriction A' to run into the interior of the inner glass E from which it will
now run at a much slower rate through the small opening E' back into A' so that
assuming that the area of the opening A' has been correctly proportioned to that
of E' by turning the stem B as described, then by the time the sand has run back
entirely, the development will be completed.
Another arrangement for facilitating the carrying out of the invention is shewn
at Fig. 2; this consists.simply of a clock G, preferably with a ten minutes dial,
on the back part of which is a circular slide rule H I of well known arrangement
for facilitating the multiplication of the time of first appearance with the before
mentioned factor, H being a fixed minutes scale, while I is the moveable scale
having divisions representing the different factors corresponding to different
developers and having a pointer I which when operating is brought to the time
division representing the first appearance, whereupon the division representing the
particular factor employed will stand opposite the division on H representing the
total time for complete development.
The glass face Jis rotatable in front of the dial, and carries an index J', which is
turned round so as to be brought over the division representing the calculated
time, so that when the pointer of the clock arrives at such index, the development
will be completed.
It will be evident that instead of timing the development by the time of first
appearance of the negative image on the actual plate to be developed, the time of
first appearance may be observed on a piece of a standard sensitive plate which has
received a standard amount of exposure to a standard artificial light, and which is
subjected to the action of the developer simultaneously with the negative, and the
development of the actual negative be calculated from such time of appearance on
the standard plate. By this means over and under exposed negatives will all
receive the same amount of development, which in practice has been found to be a
correct mode of proceeding.
I have ascertained by experiment that the following different kinds of developers
require the multiplying factors set against them :
Factor

page_text: With most developers the multiplying factor need not be changed if the developer
is diluted, but when using pyro or amidol any dilution of the developer will require
an increase of the factor. This exception in the case of pyro and amidol to the
general rule is no inconvenience in practical work when the fact is known.
The factor of any developer not mentioned above can be readily ascertained as
follows:-
In developing a negative, first note the time of appearance, then develop
according to judgment and note the total time of development. If the negative
produced is found to be satisfactory when fixed then set the pointer I¹ of the slide
rule I Fig. 2 to the division on H corresponding to the time of appearance noted;
opposite the division on H corresponding to the total time of development will then
be found the division on I representing the multiplying factor.
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. In the development of photographic negatives, the method of timing the
complete development, by ascertaining, after pouring on the developer, the time
which elapses between such pouring on and the appearance of any one part of the
image, then multiplying that time by a previously ascertained factor for the
developer employed, and arresting the development at the expiration of the time so
determined, the value of the said factor being previously determined for different.
developers, substantially as described.
2. The use for determining the time required for the complete development of a
photographic negative, of an instrument so arranged as to first give an indication
of the time that elapses between the pouring on of the developer and then to have
its action varied so as to give a second indication of time which shall correspond to
that required for the complete development, substantially as described.
Dated this 31st day of August 1894.
ABEL & IMRAY,
Agents for Applicant.