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When the matrix is thus formed, the engraving is withdrawn from the solution of metal, and the matrix substituted; the galvanic action is again renewed; a deposition of the metal upon the matrix now takes place; and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 he 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 Athenaeum, 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.
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.
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 net-work 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.
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. I .
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.
No. 5. is a polytype copy in type metal from the same matrix as No. 4. These impressions are placed in juxtaposition, for the purpose of giving an opportunity of comparing them, and forming a true estimate of their respective merits1).
There have been many attempts in London to obtain an electrotype copy of a page of types, but hitherto, I believe, without success; the difficulty arising from the deposition of copper getting under the projecting parts of the kerned letters, and also penetrating into the interstices between the letters and the words, and thus preventing the mould from being disengaged from the types, without using force and destroying a great number of letters. The following, No. 6., is an imperfect specimen of a page of diamond types, by Mr. Robert Branston, an engraver of eminence in wood, and Mr. Warren De la Rue. There are many difficulties yet to be overcome in the process of obtaining electrotype copies of types; but it will show what has already been accomplished, and I have not the least doubt that the combined skill and perseverance of Mr. Branston and Mr. De la Rue will in a short time overcome those difficulties, and produce perfect copies with ease and certainty.
The method adopted to procure this was as follows: — A mould in plaster of Paris was first obtained, and a stereotype plate was cast in it; high spaces and quadrats were used, to prevent as much as possible the inconvenience before spoken of; a mould was then obtained from the stereotype plate by the polytype process, in type metal, and from that mould, by the galvanic action, the electrotype copy from which the specimen No. 6. was printed.
In the first instance, the plan recommended by Mr. Spencer in the Athenaeum of the 4th of July, 1840, of preparing the surface of the mould with silver, was adopted, but the sulphuric acid acted on the plaster of Paris of which it was formed, and rendered it useless.
Since the preceding was written and in print, I have been informed that Mr. Spencer has been more successful than the London experimenters, for, in a letter to me, dated Glasgow, September 17th, 1840, he says, “Had I been at home I should have sent you a copy of the first pamphlet, where you would have seen an octavo page of stereotyping by the Voltaic process.”
In the present early state of electrotyping we find that, as it is formed by the solution in water of a salt composed of sulphuric acid and copper, it is of course thinner and the copper more attenuated than type metal is when in a state of fusion; it will necessarily penetrate into all the delicately engraved parts of a subject more completely than melted metal, and must therefore produce a more perfect facsimile than a casting.
I believe this is undeniable, for copies of copper plate engravings of great fineness have been produced in the highest state of perfection as facsimiles. Another point is, that copper is tougher than type metal, and not so liable to have the letters break off and fail in the process of printing, and of consequence will be more durable. But it appears to me that one of its most valuable applications will be to the printing of Bibles, for by obtaining copper matrices of the pages by this process new editions may be multiplied to any extent, and when the plates are much worn they may be renewed at any future time, without incurring the expense of recomposing the book; which is not the case with stereotype plates. But the applicability of the discovery is as yet in its infancy, as these specimens are, I believe, the first that have been published of impressions of letterpress electrotype plates, and the ingenuity of man is at work to extend and improve the discovery.
In giving the foregoing account of experiments that have been made on this discovery of the application of galvanism to the production of copies of the works of art, and more particularly with respect to engravings on wood, as connected with letterpress printing, to which this work is confined, it is evident that the persons making these experiments are not availing themselves of the information which may easily be procured, that is, of ascertaining what are the requisites to enable a printer to make use of these copies in the regular way of business; excepting this be done, the discovery will not be available for general purposes, and will be viewed only as a curiosity.
One point, to which I would particularly draw their attention, is the difficulty experienced in separating the matrix from the original, and again of separating the copy from the matrix; in both these cases they have the deposition of copper too thin, and in the act of separation both the matrix and the copy are twisted and distorted; they are then filled in at the back with some soft metal, which is planed in a rough manner, and delivered in this condition, unfit for the press, at which it is almost impossible to obtain a good impression. I would suggest that the deposition of copper should be continued for a longer time, so as to have the metal thicker, both in the matrix and the copy.
If any irregularity in the surface then take place in the act of separation, it ought to be reduced before it is filled in with metal at the back; when that is done it should be turned in a lathe, as stereotype plates now are; it would thus be of an equal thickness throughout without any unevenness on the surface or back, and when mounted type-high might be printed without more trouble than wood cuts or stereotype plates are; thus enabling the printer to produce impressions without difficulty that would show the merits of the discovery in a fair manner, which at present cannot be done without great trouble and loss of time.
No. 1 . An Impression from an Engraving on Wood.
No. 2. An Impression from an Electrotype Copy of No. 1.
No. 3. An Impression from an Engraving on Wood.
No. 4. An Impression from an Electrotype Copy of No. 3.
No. 5. An Impression from a Polytype Copy of No. 3.
No. 6. An Impression from an electrotype Copy of a Page of Diamond Types.