transverse piece, placed behind the tympans, to support them at a
proper angle when they are turned up. The transverse piece is nearly
as long as the tympans are wide, so that the frame can rest upon it:
they are inclined towards the tympans and form an abutment, and are
placed in sockets so as to be easily taken out when necessary.
GALLOWS SOCKETS.
Two pieces of wood with square mortises in them, to receive the ends
of the gallows; they are nailed or screwed upon the plank behind the
tympans. The mortises are inclined towards the tympans.
GALVANISM.
Another great discovery has been published, in addition to those
important ones of Sir Humphry Davy, which he made at the Royal
Institution, of the decomposing powers of galvanism, the brilliant
effects of which, I well remember, excited wonder and astonishment
in the crowded audiences that assembled in the lecture room of that
establishment.
The one that is the subject of the present article, promises to
be of great utility in the arts, by giving the means of obtaining
facsimiles of engraved copper plates, of engravings on wood, of
coins, medals, embossings, in short, of any engraved article, whether
in cameo or intaglio. The productions by this process have been named
_Electrotype_.
This is effected by placing the object to be copied in a solution
of any metal, when the galvanic action precipitates the metal from
the liquid that held it in solution, upon the engraving that is
to be copied. This precipitation or deposition assumes the form of
a cake of pure metal, with every line, however delicate, and every
inequality, however minute, on its surface, so as to form a matrix or
mould in the highest state of perfection.
When the matrix is thus formed, the engraving is withdrawn from the
solution of metal, and the matrix substituted; the galvanic action is
again renewed; a deposition of the metal upon the matrix now takes
place; and the result is, a perfect facsimile of the original.
This is a short sketch of the principle of this discovery. It
belongs to chemistry rather than to printing, to explain why the
metal is precipitated in a solid mass and not in a fine powder; but
such is the fact. The discovery has been applied to the production
of facsimiles of engraved copper plates with the most complete
success; and as it is now in a state of progress to produce copies
of engravings on wood, and pages of types, so as to be applicable
to letterpress printing, I will endeavour to give the present state
of knowledge with respect to this application of the discovery, the
process, and also specimens.
It is said that the discovery of this application of galvanism
originated in perceiving a thin deposition of copper at the bottom
of a galvanic battery, which, on being removed, displayed on its
under surface a perfect cast of the bottom of the cell, and suggested
an extended application. Be this as it may, the fact was noticed
by Mr. Warren De la Rue, of Bunhill Row, in a communication to the
Philosophical Magazine of September, 15, 1836, (vol. 9. p. 484,)
where he says, “The zinc plate is always partially covered with a
coating of copper, which, however, is not detrimental to the power
of the battery: the copper plate is also covered with a coating
of metallic copper, which is continually being deposited; and so
perfect is the sheet of copper thus formed, that on being stripped
off, it has the polish and even a counterpart of every scratch of the
plate on which it is deposited.” The discovery of the application is
claimed by two persons, M. Jacobi, a Russian, and Mr. Thomas Spencer
of Liverpool. The latter presented a pamphlet containing the results
of his discovery, and an account of his experiments, to the British
Association in 1839, at which time M. Jacobi’s specimens were present
and exhibited at the same meeting. Mr. Spencer has since prosecuted
his experiments, and liberally given the details and the results
to the public, in different publications; so that it is in fact to
this latter gentleman that we are indebted for our information on
the subject; but as it is now in the hands of a number of persons
of ingenuity and ability, who are prosecuting experiments on it,
there is little doubt but that it will soon be brought to a state
approaching nearly to perfection.
As copper is usually employed for engravings, and is equally
applicable to letterpress printing as to that of the rolling press;
as it is easily obtained in solution, and is not an expensive article
for this purpose, the process as here described is with that metal;
other metals have been used for experiments, and it has been stated
that articles in silver or gold may be produced with equal facility
where facsimiles of them may be required, but the production of them
in gold is doubtful.
In the process there are various things to be considered. Among
which may be particularly mentioned the fact, that the solidity of
the deposited metal entirely depends on the weakness or intensity
of the electric action. This action may be regulated by increasing
or decreasing the thickness of the plaster of Paris which separates
the two metals, and by the coarseness or fineness of the material.
Mr. Cooper states, “I made three similar experiments, altering
the texture and thickness of the plaster each time, by which I
ascertained that if the plaster partitions were thin and coarse, the
metallic deposition proceeded with great rapidity, but the crystals
were friable and easily separated; on the other hand, if I made the
partition thicker, and of a little finer material, the action was
much slower, and the metallic deposition was as solid and ductile as
copper formed by the usual methods; indeed the action was exceedingly
slow. I have made a metallic deposition apparently much harder than
common sheet copper; but more brittle.”
A friend of mine used a common garden pot, with a cork in the
perforation through the bottom, which answered very well, the copper
deposited being fine and tough. I think a wine cooler would be a good
vessel for that purpose, being porous; and either may be at hand,
when there is not a suitable glass, or any plaster of Paris.
Mr. Crosse has stated, in the account of his experiments on the
crystallization of metals, that he succeeded best when the solutions
were kept at a boiling temperature; and Mr. Spencer informs us, that
by keeping the solutions he employed at a temperature of from one
hundred and twenty to one hundred and eighty degrees of Fahrenheit,
he was able to abridge the time otherwise required, three or four
fold.
In all scientific experiments, care and attention are requisite for
a successful result: in this instance, let an uninterrupted circuit
be maintained for the electricity, and let the wire have a perfect
metallic contact with the plates which it connects; when it is an
engraving on wood, bore a hole in the side of the block, and insert
the wire in it. The zinc may be with advantage occasionally taken
out of the saline solution during the operation, and cleaned in
water. In the choice and application of the plates, it is better
that they should be, as nearly as possible, of the same size, and it
is of importance that the zinc should be as thick as the required
deposition of copper, but it is easy when necessary to renew the
zinc again and again. That the solution of the sulphate of copper
may be continued in the necessary state, crystals of that substance
should be occasionally added. When the process is long continued, the
solution should be changed, for the sulphuric acid, which is set free
by the deposition of the metallic copper, prevents the further action.
This was the first method; the plan now practised, to prevent any
stoppage of the galvanic action by an excess of sulphuric acid
occasioned by the decomposition of the sulphate of copper and the
deposition of its copper in a metallic state, is to put into the
acid a piece of copper in connexion with the positive pole, and
thus, as the acid is set free by the galvanic action, it forms a new
combination with the copper, and continues the supply of the sulphate
without the necessity of changing the contents of the vessel.
In obtaining casts by this process, it must be borne in mind, that
no metallic deposition can be made by voltaic electricity without
the presence of a metallic surface or nucleus upon which to deposit:
but this metallic surface should be given only to the part which is
to be copied; the sides and bottom of the block may be covered with
a varnish composed of shell lac dissolved in spirit of wine, which
will prevent any metallic deposition from taking place upon those
parts, as also the moisture from penetrating into the wood, and the
deposition will in consequence be confined to the engraved surface.
In the management of the simple apparatus which is employed in
electrotype, it is necessary to have the binding-screws, wires, and
all the metallic surfaces, quite clean and bright, as also to avoid
touching with the fingers that part on which the metal is to be
deposited.
With regard to the first application of galvanism to the production
of facsimiles of engravings on wood, Mr. Spencer states, after
the publication of his pamphlet, “The wood engraving being given,
take a piece of lead the required size; let its superfice be about
one-eighth of an inch larger all round than that of the wood block.
The lead must now be planed, just as a piece of soft wood; (the tool
termed by a joiner _a try plane_ does best;) a clear bright surface
is thus obtained, such as I have been unable to get by any other
means. The engraved surface of the wood must now be laid on the
planed surface of the lead, and both put carefully in a press; should
the engraving have more than two inches of superfices, a copying
press is not powerful enough. Whatever press is used, the subject to
be copied must be cautiously laid in the centre of the pressure, as
a very slight lateral force will in some degree injure the process;
the pressure to be applied regularly, and not with a jerk. When
the pressure is deemed complete, they may be taken out, and if, on
examination, the lead is not found to be completely up, the wood
engraving may be neatly relaid on the lead, and again submitted to
the press, using the same precaution as before. When the lead is
taken out, a wire should be soldered to it immediately, and it should
then be put into the apparatus without loss of time, as the less it
is subjected to the action of the atmosphere the better: care should
also be taken not to touch the surface with the fingers.”
Mr. Spencer also states that plumbers, who have handled lead for
the greater portion of their lives, are astonished to find it so
susceptible of pressure. On the contrary, wood engravers did not,
until now, imagine that their blocks would stand the pressure of a
screw press on a lead surface without injury; but such is the fact
in both instances. In the manner in which box wood is used for wood
engravings, being in horizontal sections, it will sustain a pressure
of 8,000 lbs. without injury, provided the pressure is perfectly
perpendicular.
Mr. Spencer has omitted to mention the size of the engraving; if it
were one inch square, it would have a pressure of 8,000 lbs. on that
inch; if it were nine inches square, it would only have a pressure
of 100 lbs. on the square inch: with my experience of printing
engravings on wood, I would not venture to submit one to a pressure
of 8,000 lbs. to the inch for fear of crushing the lines. I mention
this as a caution; it may prevent an accident.
This appears to have been the first method tried to produce a
facsimile of an engraving on wood by means of galvanism, with a
metallic mould obtained by impressing the engraved block upon a
piece of lead. This not appearing to be perfectly satisfactory,
other persons were induced to endeavour to make the discovery
available for letterpress printing without the risk of injury to the
engraving, to which this plan seemed liable; and the next advance
towards the perfection of the process was an important one, being
the introduction of the real object intended to be copied in the
stead of the substituted mould, and obtaining a matrix from it at
once by means of the galvanic process without resorting to any
intermediate measures. This improvement was made by Mr. Robert
Murray, who proposed “in January last to cover the surface of the
wood with plumbago [black lead], so as to render it a conductor; and
then to proceed in the usual manner for obtaining an electrotype
copy,” as he informed me in a communication of the 21st of July,
1840. It is but fair to state, that this use of black lead has been
objected to by some engravers on wood, as having a tendency to fill
up the lines of a delicate engraving, and so to deteriorate the
impressions taken from it; but I am now furnishing the public with
the means of deciding on this question, by presenting an impression
from an electrotype copy, executed by Mr. Murray according to his
own ingenious plan, by the side of one from the original wood
engraving, and I leave it to bear witness for itself. I cannot
perceive any deterioration in the copy, nor any difference between
the two impressions: in fact they appear as if they were duplicate
impressions from the same engraving.
The following letter, addressed to the editor of the Athenæum, by
Mr. Spencer, which appeared in that publication on the 4th of July,
1840, details another method of obtaining a metallic surface for
an engraving on wood, &c. for the purpose of inducing the galvanic
deposition of copper upon it and obtaining a copper mould, which
appears to be free from the objections that have been raised to
gilding, bronzing, and to black lead.
“In my pamphlet, printed last September, I there stated I considered
the process comparatively incomplete, unless we were able to apply it
to the multiplication of models in clay or wood, castings in plaster,
wood engravings, &c., as the fact, that galvanic deposition always
requires a metallic surface to act on, seemed to set bounds to those
branches of its application. I then resorted to various expedients
to surmount the difficulty; among others, that of gilding and
bronzing the surfaces of such materials to a limited extent: this was
successful, but still troublesome and expensive, and, more than all,
the sharpness and beauty of the original was necessarily injured. I
have since attempted to metallize surfaces by the use of plumbago
(suggested to me many months ago by Mr. Parry of Manchester).
“Should I be desirous of obtaining a copper mould or cast from
a piece of wood, plaster, or clay, or, indeed, any non-metallic
material, I proceed as follows:--Suppose it is an engraved wooden
block, and I am desirous of metallizing it, in order that I may
be able to deposit copper on its surface (this example will hold
good for any other material), the first operation is to take strong
alcohol in a corked glass vessel, and add to it a piece of phosphorus
(a common phial corked will answer the purpose); the vessel must now
be placed in hot water for a few minutes, and occasionally shaken.
By this means the alcohol will take up about a 300th of its bulk
of phosphorus, and we thus obtain what I would term an alcoholic
solution of phosphorus. The next operation is to procure a _weak_
solution of nitrate of silver; place it in a flat dish or a saucer;
the engraved face of the block must now be dipped in this solution,
and let remain for a few seconds, to allow capillary action to draw
it into the wood.
“This operation being performed, a small portion of the alcoholic
solution of phosphorus must now be poured in a capsule or
watch-glass, and this placed on a sand-bath, that it may be suffered
to evaporate. The block must now be held with its surface over
the vapour, and _an immediate_ change takes place; the nitrate of
silver becomes deoxidized and gives place to a _metallic_ phosphoret
of silver, which allows the voltaic deposit to go on with as much
rapidity and certainty as the purest silver or copper.
“The whole process may be performed in a few minutes, and with
absolute certainty of success. The interior or exterior surface of
a plaster or clay mould of a statue, no matter what size, may be
thus metallized with equal facility. For the process of vaporizing,
and should the material to be acted on not be very large, I prefer
fastening it to the top of a bell glass receiver with a bit of pitch
or cement, and thus placing it _over_ the capsule on the sand-bath;
the phosphoric vapour is by this means equally diffused and not
dissipated. An ethereal solution of phosphorus also answers; and a
solution of either of the chlorides of gold or platinum may be used.
I am inclined to think this process, independent of its uses in
galvanic precipitation, may be applicable to other branches of art. I
would recommend those curious of testing its effects, to try a small
and sharp plaster of Paris medallion: dip its _surface_ in a weak
solution of nitrate of silver and _take it out immediately_; fasten
it to the bottom of a glass tumbler, and at the same time have a
little hot sand ready in a dish; lay the watch glass containing a few
drops of the phosphoric solution on it; now place the mouth of the
tumbler over all, and the medallion will be observed almost instantly
to change colour. The operation is now completed. A piece of pottery
ware in the state of biscuit may be acted on in a similar manner.
“_Liverpool, June 27._ THOMAS SPENCER.”
_Apparatus and process._--The annexed figure and explanation will
afford an example of the action of a voltaic apparatus, and will be
sufficient to render the subsequent details intelligible. A is a
vessel filled with a solution of common salt, which is a compound
of chlorine and sodium; B is a tube immersed therein, closed at
the lower end with a piece of bladder stretched over it and firmly
tied; this tube is filled with a solution of blue vitriol, that is,
a compound of sulphuric acid and oxide of copper. A plate of copper
C, and one of zinc Z, connected by means of the wire W, are immersed
in those fluids. The zinc decomposes the salt, with the chlorine
of which it unites, forming chloride of zinc, while the sodium of
the salt is repelled, and passing through the bladder, enters the
solution of sulphate of copper, which it decomposes, uniting with the
sulphuric acid and oxygen to form sulphate of soda, and setting free
pure copper in the form of beautiful crystals, which are deposited on
the plate C. The connecting wire W serves to convey electricity from
C to Z, and thus the action is maintained so long as any common salt
and sulphate of copper remain undecomposed.
[Illustration: Apparatus for galvanic action]
Mr. Spencer’s first attempt was made with a piece of thin copper
plate, which he covered with a cement of beeswax, resin, and Indian
or Calcutta red. The plate received its coating while hot, and on
becoming cool, the experimenter scratched the initials of his name
upon the plate, being careful to clear away all the cement from the
scratches, so as to expose the copper below. A piece of zinc was
attached to this plate by a copper wire, and the voltaic current was
set in action by means of the simple apparatus shown in the adjoining
figure.
A may be supposed to represent a glass vessel of convenient form. B a
gas glass stopped at the lower end P, by a piece of plaster of Paris,
to the depth of three quarters of an inch, Z a plate of zinc, and C
a similar piece of copper, a coin or any other metallic substance to
be acted upon; and these two are connected by a copper wire, W. The
inner vessel may be kept in its place by a cork, or any other means
that may happen to be more convenient. A solution of sulphate of soda
is poured into the gas glass, and the wire connecting the zinc and
copper plates being bent, as shown in the figure, the zinc plate is
immersed into the solution of sulphate of soda, and the copper plate
into the solution of sulphate of copper.
[Illustration: Another apparatus]
In a few hours Mr. Spencer, in his experiments, found that the
portion of the copper rendered bare by the scratches was coated
with the pure bright deposited metal, while those portions which
were still covered with cement were not acted on. It now became an
important inquiry whether the deposition would retain its hold on the
plate, and whether it would be of sufficient solidity to bear working
from; that is, supposing an etching or engraving to be made, and the
lines to be afterwards filled up with copper by the voltaic process,
whether such lines could be printed from.
In order to answer this last question, Mr. Spencer coated with cement
a piece of copper, and with a steel point endeavoured to draw lines
in the form of network, so as to penetrate the cement and expose the
copper. After this plate had been exposed to voltaic action, and then
heated, so as to get off the covering of cement, the copper network
came off with it. This happened many times; but by an accident it
occurred to the experimenter to employ nitric acid to the plate,
after it had been cemented and engraved on as before. It was then
subjected to the voltaic process for forty-eight hours, when the
lines were found to be entirely filled with copper. On applying heat,
and then turpentine to get off the cement, it was found that the
voltaic copper had completely combined with the plate on which it was
deposited.
A plate was then coated with cement, and lines worked upon it by an
engraver; but these lines were of a wedge-shaped form, leaving only a
hair line of the copper exposed at the bottom, and a broad space near
the surface; and where the turn of the letters took place, the top
edges of the lines were galled and rendered rugged by the action of
the graver. All this was objectionable; but another plate, similarly
prepared, and engraved on with a sharp point, had the copper
deposited on the lines; and this was printed from successfully.
This was an attempt to deposit lines upon a plate of copper by the
galvanic action, and thus form an engraving in relief, which I have
doubts of being successfully practised with finished subjects.
The application of heat separates the two metals, in consequence of
their different expansibility when subjected to its influence.
Mr. Spencer gives the form of another apparatus on a more extended
scale, which he recommends, as it may be employed in large works.
[Illustration: Larger scale apparatus]
A is an earthenware vessel to receive the copper plate and the
solution of sulphate of copper, in which it is to be exposed. B
is another vessel of earthenware or wood, of such a size that it
may fit into the outer one, as shown in the drawing; the bottom of
this vessel being formed of plaster of Paris, or some other porous
substance, which while it retains the solution of common salt may
permit the voltaic action to go on without impediment. C is the
copper plate to be acted on by the electricity upon which copper
is to be deposited. Z is the zinc plate, and the two are united by
the wire W, which may either be done in the manner exhibited in the
second engraving, or by the use of a binding screw S.
I have been anxious to give specimens of this discovery in its
application to letterpress printing, with some account of the process
by which copies are obtained from engravings on wood. I am gratified
in being enabled to do this, and to give two subjects, by different
processes in producing the matrices or moulds.
No. 1. is an impression from an engraving on wood by the late Mr.
Branston, which I give for the purpose of comparing the copy with
the original. From this engraving Mr. Murray, having metallized
the surface with plumbago, according to his method, to induce a
deposition of the copper upon it, obtained a copper mould by galvanic
action; from this mould No. 2. was produced by the same process, and
is an impression from the electrotype copy of No. 1.
No. 3. is an impression from an engraving on wood, from which a
matrix was prepared in type metal by the process called _polytype_;
this matrix was submitted to the galvanic action by Mr. Murray, and
the deposition of copper produced the electrotype copy from which the
impression No. 4. is printed.