AN IMPROVED FORM OF DEVELLOPING BATH ESPECIALLY FOR LARGE PHOTOGRAPHIC PRINTS
Year: 1886

page_text: Date of Application, 4th Mar., 1886.
Complete Left, 4th Dec., 1886.
Complete Accepted, 14th Jan., 1887.
BENJAMIN HOWARTH THWAITE F.C.S. 37 Victoria Street Liverpool in the County
of Lancaster Civil Engineer do hereby declare the nature of my invention for AN
IMPROVED FORM OF DEVELLOPING BATH ESPECIALLY FOR LARGE PHOTOGRAPHIC PRINTS
to be as follows:
My improvement consists in the method of forming and constructing develloping
baths, especially for large photographic prints such as copies from engineering
drawings.
I make my develloping bath in the form of a rectangular receptacle sufficiently
deep to hold prints lowered in vertically and end ways. To make the bath portable
I provide wheels on which it can run, I make the lower end or bottom of the bath
rather wider than the top, the width I usually adopt is 5 inches at the bottom of the
bath and 4 inches at the top by this arrangement I prevent the prints from becoming
attached to the sides.
On each side of the bath close to the top edges I provide drying rods, attached to
the bath by small brackets, under these drying rods I provide drip troughs into which
the moisture runs or drops from the prints when they are hung on the drying rods.
I provide draw off cocks to both the drip troughs and the bath.
For ferro-prussiate prints I construct the bath of a framework of wood lined
internally with sheet zinc.
I strongly brace the woodwork together in any ordinary manner but I usually use
hoop iron straps.
For prints in which there is required an acid develloping solution I line the inside
of the bath with any acid resisting material such as gutta percha, vulcanite enamel or
porcelain if the bath is formed of sheet iron I may enamel it or I may form the bath
entirely of porcelain or earthenware.
In order to assist or facilitate the lowering of the prints into the develloping solution
I provide simple clips such as the ordinary letter clips, these I attach to the lower end
of the print before lowering it into the solution; for acid solutions I form the clips of
vulcanite.

page_text: I provido strips of wood, pieces of glass, vulcanite or wire on which to hang prints
when in develloping solution.
I may provide a loose cover for covering the upper end of the bath to protect the
develloping solution.
The advantages of my invention are, that the bath occupies far less space than the
present form, and for ferro-prussiate prints the water can be used for weeks without
requiring any renewal, as all the salts fall to the bottom of the bath the supernatant
water is kept quite clear.
Two or three or more baths can be placed in close proximity when more than one
develloping solution is required the whole group occupying very little floor space.
The develloping process is much more rapidly effected than with the ordinary flat
bottomed bath.

page_text: Improved Form of Developing Bath, Especially for Large
Photographic Prints.
I, BENJAMIN HOWARTH THWAITE of 37 Victoria Street Liverpool in the County of
Lancaster Civil Engineer 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 improvements in photographic developing baths, particularly
of that type used by Engineers and Architects for copying their drawings by
heliographic processes.
The ordinary form of developing bath for this purpose occupies considerable
space, and is often productive of much annoyance, and has to be renewed, almost every
time it is used with fresh supplies of water, or other developing solution, otherwise the
prints become discoloured by the deposited or suspended salts.
My Invention is intended to overcome these disadvantages, and is shown on the
accompanying sheet of drawings, which is intended to form part of this specification.
Fig. 1 is a side elevation, Fig. 2 a cross section, and Fig. 3 a plan of the single
developing bath, intended for the cyanotype or ferro-prussiate prints.
a is the bath, which is filled with water or other developing solution, other than acid,
this is lined with zinc, and externally framed with wood, the prints to be developed
are lowered edgeways into the bath, and may be hung on the glass wood or vulcanite
rod b.
After the prints are properly developed, they are withdrawn, and either hung on
side rods projected from the bath or pinned to projecting side ledges c, until dry, the
water dripping into troughs d.
Both the troughs and bath are provided with regulating cocks to withdraw the
water and deposited or suspended salts therefrom.
When developing the Shawcross or Gallic acid prints I employ especially long
brushes, or I may use revolving brushes fixed lengthways, across the bath, to remove
the unacted on salts from the print by attrition.
The bath is mounted on wheels.
Figures 45 and 6 are respectively a side elevation section, and plan of a duplex
bath, one compartment of which is lined with gutta percha, vulcanite or other acid
resisting material.
Figures 7, 8 and 9, shew a triple compartment bath for the pellet or other process
requiring three developing solutions, two of the compartments are gutta percha lined,
and the other is lined with zinc.
The side divisions may be made of wood.
I provide covers for the top of bath to preserve the developing solution from dust.

page_text: To further economise space, I may combine the printing frame and the bath
together as shewn in figures 10 and 11, in which e is the bath and the printing
frame.
Having now particularly described and ascertained the nature of my said Invention
and in what manner the same may be performed, I claim
1st. The arrangement of a developing bath substantially as heroin shewn and
described for large photographic prints.
2nd. The use of one or more developing baths placed side by side substantially as
herein shewn and described.
3rd. The combination of said bath with printing frame substantially as herein
shewn and described.