Process of and Apparatus for Producing Etched Metal Plates.
Year: 1899

page_text: [The Amendments are shoum in erased type.]
Date of Application, 7th Feb., 1899-Accepted, 18th Mar., 1899
Communicated from abroad by MAX LEVY, of No. 1213, Race Street, Phila-
delphia, County of Philadelphia, and State of Pennsylvania, United States
of America, Manufacturer of Specialties for Photo-Engravers.
Process of and Apparatus for Producing Etched Metal Plates.
I, WALLACE FAIRWEATHER, C.E., of 62, Saint Vincent Street, in the City of
Glasgow, Chartered Patent Agent, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
-
This invention relates to a process of and apparatus for producing etched metal
plates, more particularly such metal plates as are used in photo-mechanical
engraving.
The object is, by the employment of a mordant, to produce a printing surface
upon metal in which the indentations or lines produced as the result of the
process are of a more perfect character than those produced by the means
ordinarily used; also to reduce the cost of production and obviate many of the
objections incident to the processes and means heretofore employed.
The present invention includes an essentially new process of applying the
mordant to a prepared plate, which mordant is projected and atomized upon
the plate so as to form therein, where not protected by the resist, and after
a certain depth is etched out, cupped or concave indentations or lines. The
carrying out of the process embodies the use of compressed air and ejector
nozzles for projecting the mordant in the form of an atomized spray upon a
prepared metal surface, so that the mordant which is impacted thereon will
drop therefrom without flowing. The chemical combination of the mordant
with the metal is accellerated by the dynamic force of the impact, which causes
each atomized particle of the mordant to become practically saturated with the
metal base instantly upon contact, this results in eroding or cutting away the
metal in the direction of the impact faster than the same action proceeds
laterally, so that much or all of the required vertical depth may be etched before
the lateral action of the mordant can materially affect the work; moreover, the
forcible impact of the atomized spray, besides accellerating the chemical com-
bination of the mordant and the metallic base, prevents the adhesion to the

page_text: plate of the bubbles of hydrogen gas and the scum of metallic oxide which are
developed by the chemical action, and which in ordinary practice are removed
by the workmen with a brush; also by the use of compressed air for projecting
the mordant, the heat evolved by the chemical action of the mordant on the
plate is absorbed, keeping the mordant and plate cool, so that a stronger
mordant than is usually employed can be used without detriment to the resist.
In the accompanying drawings which show one form of apparatus designed
to carry into effect this new process of etching:-
Figure 1 is a side elevation.
Figure 2 is a plan view.
Figure 3 is a sectional view on the line 3-3 of Figure 1.
Figure 4 is a vertical section on the line 44 of Figure 1.
Figure 5 is a longitudinal section on the line 5-5 of Figure 2, and;
Figure 6 is a vertical sectional view, showing a preferred form, of one of
the atomizing-nozzles detached.
In the apparatus illustrated, there is placed upon a stand an acid proof tank A.
for the mordant, which tank has a valved inlet pipe a and an outlet pipe «¹,
the latter being preferably provided with a branch pipe a², for the purpose
of maintaining a predetermined level of the mordant or etching-fluid in the
tank. The etching-box or chamber B rests upon the bottom of the tank A
which has openings through its sides below the normal level of the mordant,
so that an air chamber B positioned at the bottom of the etching-box will be
submerged in the mordant, to surround the nozzles or atomizers b, which project
from the top of the air chamber. The nozzles or atomizers beach have a cen-
tral passage to the air chamber, and a plurality of ducts for the mordant, the
lower ends of said ducts in use being submerged in the mordant. The openings
in the nozzles preferably taper and above the point of convergence the nozzles
are recessed, as shown. A suitable distance above the nozzles or atomizers, the
etching-box is constructed to support slides C, which receive a board to which
the plates prepared for etching are secured, and attached to the etching-box,
adjacent to the openings through which the slides are inserted, are springs c,
with which turn-buttons e', carried by the slides may be placed in engagement,
and the etching-box on the opposite side from the springs, has sockets or guides
in which are mounted so as to be reciprocated, pins ². The top and sides of
the etching-box are preferably transparent, and to carry away the fumes and
provide for a circulation of air there is attached to the etching-box a ventilat-
ing pipe B³
Adjacent to the etching-box is a washing compartment D, the sides thereof
having grooves or ledges so that the slides may be moved from similar grooves
or ledges in the etching-box into the washing compartment, to be positioned
over a series of perforated pipes B₁ which are connected to a water supply, so
that water under suitable pressure may be projected upon the plate, to remove
the mordant therefrom, and to the bottom of the compartment is secured a waste
pipe d.
To supply compressed air to the air chamber B and to the nozzles thereof,
an air compressor or pump E is mounted on the stand and connected to an air
tank E, from which air under compression is taken by a pipe e, through a three-
way cock and pipe e¹, to the air chamber in the etching-box. The cock fis
connected to a pipe g, which extends therefrom to the upper part of a water
tank G and to the lower part of the tank is attached a pipe which communi-
cates with a three-way cock i, said cock being connected with a water supply
pipe and to a pipe k, which is in communication with perforated pipes 11,
in the bottom of the water compartment. To the pipe is secured a connection
or small pipe which leads into the pipe g just before it enters the tank, for
the purpose of preventing the water rising above the upper portion of the pipe g¹
and entering the pipe g. The several pipes may be provided with check valves
to prevent any back flow of air or water therein. The three-way cocks f and i

page_text: are provided with handles which are connected to each other and to a lever by
a rod, so that the cocks may be turned in unison.
The cocks are so adjusted that while the cock f is open to let the air pass
into the pipe el, the cock i is open to let the water pass from the supply pipe k
through the pipe to the reservoir G, and when the lever is pulled back the
cock is closed to pipe e¹ and opened to pipe g, and the cock i is closed to the
pipe and the reservoir G, and opened to let the water pass to the pipe k' and
thence to the perforated pipes D¹. Near the air pump E so as to engage with
a pulley on the pump shaft, is mounted a friction-wheel L and on the shaft
which carries said friction-wheel is an eccentric disk L', positioned so as to
engage with pins which abut against the slides, and when the disk is turned
one of the slides C, which has been placed in engagement with the spring c
attached to the etching-box, will have imparted thereto a reciprocating move-
ment which changes the position of the plate to be etched with respect to the
nozzles of the atomizers, so that the greatest dynamic force and quantity of the
atomized mordant will be distributed equally over the surface of the plate,
instead of immediately above the nozzles.
In carrying the invention into effect, with the apparatus shown, the plate is
prepared in the usual manner being coated or covered with a resist except where
the mordant or etching-fluid is to act. The plate or several plates to be etched
are attached to a board which is placed in the upper slide, the same being
passed into the etching-box so that the plates will be supported therein face
downward. By turning the three-way cocks, compressed air from the air tank
is let into the air chamber of the etching-box and escaping through the nozzles,
atomizes and projects the mordant in the form of spray upon the plates carried
by the slide, which is actuated in one direction by the springs, and in another
direction by the pins which engage therewith, the pins being actuated by the
disk L', to which a rotary motion is imparted.
After the closer lines have been bitten in the plate to the required depth,
the plate is removed from the etching-box and washed, and the lines are then
protected by a resist or varnish, after which the board and plate attached thereto
is placed upon the lower slide and again inserted in the etching-box, so as to
have the mordant impacted upon the plate with greater force and quantity, to
deepen therein the wider depressions.
The etching-box is constructed so as to provide practically a closed chamber,
and the boards which carry the plates when placed therein reduce the area of
the chamber in which the air under compression enters through the nozzles
to project the mordant, and the air when separated from the mordant, escapes
through the ventilating pipe, which enters the chamber beneath the lower slide,
said ventilating pipe carrying away the fumes created by the chemical action
of the mordant on the metal.
When the slide carrying the plate is moved over or into the washing com-
partment, the three-way cocks are turned by the lever, so that compressed air
is let into the upper part of the water chamber to give the requisite pressure to
the water therein, so that it may be projected with force through the perforated
pipes and upon the plates, washing the latter free from what acid may remain
thereon.
In some character of work, the plate may be etched to a sufficient depth
without applying other than the original resist thereto and in such work the
position of the plate in the etching-box with respect to the distance from the
atomizing nozzles may be varied as the etching proceeds.
In practice, the etching fluid is impinged upon the plate in the form of
spray of minute particles which do not affect that portion of the plate which is
covered by the resist, but where the design on the metal is more or less broadly
exposed, the mordant or etching fluid collects and adheres depending therefrom
in the form of spherical drops which are constantly being added to by fresh
accretions. The mordant which thus adheres to the plate is kept in motion

page_text: by the impact of new particles of the spray and the saturated solution of the
mordant goes to the lower portion of the depending globules so that what is
removed from the plate falls immediately therefrom. The tendency-of-a-drop
of etching fluid-or-mordant depending from a plate maintained in a horizontal
position is-to-assume-a-spherical form, and this of itself after the plate has
been eroded to such depth as to give effect to the drops, tends to ent-a-concave
er-cupped-depression while avoiding Interal erosion or undercutting. Etching
by projecting the mordant in the form of spray upon the metal effects a great
gain in rapidity of operation over the methods usually practiced, as a much
stronger etching-fluid may be used. The chemical action of the mordant pro-
ceeds faster vertically or in the direction of the impact, than otherwise; the
impact of the minute particles of the mordant does not disturb the resist which
forms the design, and the heat generated by the chemical action of the mordant
upon the plate is absorbed by the compressed air as it expands, which keeps
the mordant and plate cool. With the apparatus shown, the air which has been
previously compressed is allowed to expand and circulate in the etching-box, so
that the etching-fluid which drops from the plate passes through a body of
cooled air into the tank from whence it was taken, and the fumes which are
given off by the process of etching are carried away by the ventilating pipe.
The apparatus which I have shown is one which may be used for commercially
carrying out the process and it may be varied in many particulars, for instance,
where water under sufficient pressure can be had, the water tank and connec-
tions therefrom may be dispensed with; other means may be used to supply
compressed air to the nozzles of the atomizers, and any suitable form of atomizer
may be used for projecting the mordant upon the plate.
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:-
1st. The process of etching-metal-plates, which consists in atomizing or
spraying a mordant, by means of compressed-air-against the face of a plate having
thereon-the-design-through-a-resist, so that the dynamic-force of the impact will
necellerate the chemical nation of the mordant, and the compressed air absorb the
hent-generated by the chemical action of the mordant, for the purposes set forth.
2nd. The process of etching metal plates, consisting in projecting by-means-of
compressed air-a-mordant which-is-atomized-upon a plate having thereon the
design-to-be-etched, the mordant being impacted in the form of atomized-sprey
upon-the-plate-nt substantially-right-angles to its surface, so that the dynamie
force of the impact will not affect the resist or design, and the heat evolved by the
erosive-action-of-the-mordant will be absorbed by the expansion of the air,-sub-
stantially-as-set-forth.
3rd. The process-of-etching metal plates, consisting in-projecting by-means-of
compressed air a mordant in the form of atomized spray-upon a plate-maintained
within-a-chamber, said plate having thereon the design to be-eteled, the mordant
being impacted upon the plate at substantially right angles to its surface, so that the
dynamic force-of-the-impact-will not affect the design, and the heat evolved by the
erosive-netion of the mordant will be absorbed by the air which expands in the
chamber, substantially as set forth.
4th. The process of etching metal plates, which consists in projecting a mordant
in the form of spray from a plurality of atomizers upon the plate and moving the
plate whilst under the netion of the mordant.
6th. The process of etching-metal plates by a mordant, which consists--in
atomizing or spraying the mordant-upon-the-under-surface-of-a-prepared plate,
reciprocating or otherwise moving the plate to change-its-position-with-respect to
the atomizers, so that the chemical-action-and-dynamic force of the impacted
mordant-will-be-equal-over the surface of the plate.
6th. The process of etching-metal-plates-by-a-mordant, which-consists-in-pro-

page_text: jeeting the mordant upward within a chamber upon the under surface of a plate
maintained in the chamber co that the mordant will drop therefrom, without
flowing, through a body of released compressed air employed to project the mordant
and to absorb from it and the plate the heat evolved by the chemical action of the
mordant on the plate.
7th. The process of etching metal plates, consisting in applying to the plate a
photographically prepared design and resist, subjecting it in a chamber-to-the
nction of a-mordant which is impacted upon the plate by air under compression, the
expansion of the air absorbing from the plate and mordant the heat evolved by the
erosive nation of the mordant in-etching, and finally washing the plate, cubstantially
As set forth.
8th. The process of etching metal plates by a mordant, which consists in
atomizing the mordant-against-the-under-surface of the plate--maintained-in-a
horizontal position face-downward.
9th. The process of etching metal plates, which consists in projecting or
spraying a mordant-upward-against-a-plate supported horizontally-in-a-chamber-or
etching box
1. 10th: The process of etching metal plates by a mordant, which consists
in projecting a mordant mechanically in comminuted form upward against the
under-surface of a plate having thereon a design, which plate is maintained
face downward in a chamber, the mordant after impact upon the plate being
permitted to fall therefrom into the body of the mordant from which it was
taken.
11th. In-an-apparatus-for-etching, the combination-with an etching-box-having
means for maintaining a plate therein, of atomizers, a chamber for-compressed-air
connected-with-the-atomizers, and-a-tank for the mordant, for the purpose set-forth.
2. 12th. In an apparatus for the production of etchings, the combination
with an etching-box having means for sustaining horizontally therein a plate,
a tank for the mordant, an air chamber within the etching-box, and means for
projecting the mordant upward against the plate.
3. 13th In an apparatus for the production of etchings, the combination
with an etching-box having slides for supporting a plate, openings for intro-
ducing the slide to the etching-box, and means for reciprocating the slide, of a
tank or receptacle for the mordant, a plurality of devices within the etching-box
for atomizing or spraying the mordant upward, said devices being arranged at
uniform distances apart, and means for conveying air under pressure thereto,
substantially as shown.
14th: In an apparatus-for-etching, the combination of an etching box,-a-plate
support, atomizers for projecting a mordant upon the plate-and-means-for-moving
the plate support to change its position and the position of the plate or plates
earried thereby with respect to the atomizers.
4. 15th. In an apparatus for etching, the combination with an etching-box
and means for projecting a mordant upon a plate positioned therein, of a washing
compartment having means for projecting a fluid, and a plate-carrier which is
movable from the etching-box into the washing compartment, substantially as
shown.
5. 16th. In an apparatus for etching, the combination of a tank containing
compressed air, an etching-box or chamber having therein a plurality of
atomizers, means for atomizing a mordant by air under compression, so that
the mordant will be impacted upon the plate in the form of comminuted spray
and means for supporting and moving the plate in the etching-box, for the pur-
pose set forth.
6. 17th In an etching apparatus, an etching-box having an air chamber
with atomizers, a tank adapted to contain a mordant which surrounds the
atomizers, means for compressing air and supplying it through the air chamber
to the atomizers, a plate carrying slide reciprocally mounted within the etching-

page_text: box and removable therefrom, a water tank in communication with a water
supply and with the air compressor, a washing compartment having therein a
series of perforated pipes, and cocks for controlling the air and water supply,
the parts being organized for co-operation, substantially as shown and for the
purpose set forth.
Dated this 6th. day of February. 1899.