THE ELECTROTYPE.

An elaborate and very lucid article on the Electrotype and Daguerreotype, being a review of “An Account of Experiments in Electricity made by Thomas Spencer—Annals of Electricity, January 1840,” and of the account of M. Daguerre’s discovery of Photogenic Drawing as published by himself, has appeared in that excellent work “The Westminster Review” for September. Our space not allowing us to enter so fully into details as our admirable contemporary, we present our readers with as concise an article as the nature of the subject will permit, confining ourselves for the present to the Electrotype, as being less generally known, though not less curious.

The electrotype is another instance of the application of invisible elements to the uses of man, by which powers and influences, of whose nature he is as yet wholly ignorant, are made subservient to his purposes, and obedient to his rule.

To define accurately what electricity is, would be, as yet at least, impossible. Many conjectures have been, are, and will be hazarded, but the knowledge of its production, power, and effects, is only in its infancy, and so full of promise of a gigantic growth, that time will be better spent in its cultivation than in debating upon what it is.

The truth of this proposition is fully borne out by the subject of our present paper; for whilst many scientific men have been exhausting their energies in the production of plausible theories upon the nature of the electric fluid, other more matter-of-fact philosophers have addressed themselves to its application; and whilst some of these devote themselves to the developement of its motive powers, in the well-founded hope of its superseding steam, others press its services to far different uses. Amongst the last, Mr Spencer holds a foremost place.

Before entering into the description of the electrotype, we must say a few words on the subject of electricity to the less informed of our readers. The electric fluid, as it is called, may be produced in various ways: the most ordinary is by the friction of glass against silk, as exemplified in the electrical machine, which is familiar to almost every one. But galvanic and voltaic electricity is differently produced. In all cases its production is the consequence of combination, but particularly in the galvanic battery and voltaic circle. The latter, being Mr Spencer’s apparatus, we shall briefly describe.

An ordinary voltaic circle is formed by a plate of zinc and another of copper being placed upright in a vessel containing acid or a saline solution. Zinc is more oxidisable than copper, that is, it has a greater affinity to, or inclination to unite itself with, the gas called oxygen, the combination of which with the particles of metal produces that appearance which is called “rust.” Whilst the zinc and copper are separate, the oxygen of the fluid operates upon both; but if they are united by means of a wire connected with each, the oxygen forsakes the copper altogether, and proceeds with increased force to unite with the zinc, and a current of electricity is immediately formed, which proceeds from the zinc plate through the fluid medium to the copper, thence along the connecting wire to the zinc, and thence round again in a constant circulating stream, until the zinc has been entirely decomposed, or oxidised.

Electricity being thus produced by combination, its progress and effects are marked by a wonderful power of separation or decomposition, which it exerts upon substances brought within the circle; and this is the power which Mr Spencer has turned to his use, the great object which he has at present in view being the multiplication of engraved plates of copper for the purpose of printing from.

Every person who has seen metal of any description in a state of fusion, must have remarked that it never forms a thin fluid such as water, capable of insinuating itself into the smallest interstices, but is what would be called thick even at the fiercest heat, consequently incapable of entering into such fine scratches as are necessary to be accurately and clearly defined upon an engraved plate. Again, the contraction and expansion of all metals by the application of heat and cold, would offer an almost insuperable bar to the utility of casting, even if the fusion could be rendered perfect. But the application of electricity removes all the inconveniences, and opens a new field of science.

Mr Spencer’s apparatus consists of an earthenware vessel, in which is suspended another, much smaller, of earthenware or wood, with a bottom formed of plaster-of-Paris. Into the larger vessel is poured a saturated solution of copper (the copper being dissolved in sulphuric acid) sufficient to rise up along the sides of the lesser one, which is filled with the acid or saline solution intended to operate upon the zinc. The plaster-of-Paris being very porous, allows the two liquids to meet in its cells, but prevents them from mixing; by permitting them to meet, however, the current of electricity is enabled to circulate through all. In the larger vessel, and beneath the bottom of the smaller one, is placed the copper plate from which the cast is to be taken, or upon which the pattern is to be raised. It is suspended by the wire, which is to connect it with the zinc, being fixed on the edge of the inner vessel, in which is the zinc plate, suspended by its connecting wire. The two wires are then brought into contact, fixed together by a screw, and the voltaic circle is complete. The acid in the upper vessel attacks the zinc, the electric current descends through the plaster bottom, thence through the solution of copper, where its separating or decomposing power is brought into operation, causing the infinitely minute particles of copper suspended in the solution to separate from the sulphuric acid, and descend upon the plate, through which itself proceeds to the wire, and so round again.

Now, here is probably the most wonderful part of the process. It is only on the copper plate that the particles of copper, disengaged from the solution, will descend and settle. If the copper be varnished, or covered with a coat of wax, they will not deposit themselves or go together at all; but where they find the clean surface of the metal, they at once not only settle, but fix and adjust themselves in their proper forms, building up as it were a metal structure, not eccentric or uneven, but forming a correct plate of new metal, so pure, so hard, and so free from defect or extraneous matter, that engravers prefer copper plates thus formed to any other for working upon. But the perfection of this operation consists in the wonderful accuracy with which the finest lines of the most beautiful engravings are copied: the particles which float in the solution are so indefinitely small, that they can enter into the finest cuts, the slightest scratches; and as they undergo no process of heating or cooling, their form is in nowise altered.

We have already observed, that if the plate of metal be covered, even with varnish, the particles will not descend or form upon it; nevertheless, if some slight substance be not interposed, the depositing particles adhere so firmly to it as to be inseparable, and it is upon this property that one of the processes—that of engraving in relief on a plate of copper—entirely depends for success. When a cast of an engraved plate is required, the plate must be coated with bee’s-wax, mixed with a little spirits of turpentine. It is laid on the plate in a lump and melted, and when just cooling is wiped off, when, although apparently clean, enough remains to interpose between the new and original plates, and prevent a too strong cohesion. It is not necessary that the engraved plate should be copper: it may be for instance lead or type metal, in which case it need not be waxed, as the application of heat, expanding the metals unequally, causes them at once to start asunder.

A piece of wire having been soldered to the back of the plate, its back and edges should be covered with a double coat of thick varnish, or it may be embedded in a box with plaster-of-Paris or Roman cement. This precaution is necessary, to prevent the plate from being inclosed, and to limit the deposition to a proper extent.

It may now be suspended in the apparatus, and the wires being placed in contact, the operation begins. Particle by particle the new metal is formed, until the plate is of sufficient thickness, when it is withdrawn, and heat being applied, the two plates are separated, one being the exact counterpart, in relief, of the other. Care must be taken in all cases to change the solution of copper frequently, for by merely adding, the separated particles of the sulphuric acid would accumulate to such extent as to mar or injure the operation.

From the plate thus formed in relief, as many casts as may be required can be obtained, by making it the mould.

To copy or multiply medals and coins the operation is very simple, for a mould can be easily obtained by compressing the medal or coin between two plates of milled sheet lead, and by varnishing the lead round the impression, the deposit will be formed in the hollow only; and for this purpose a very simple apparatus will suffice, and one that may be very easily made. For the outer vessel an ordinary glass tumbler or finger-bowl will answer; and for the inner, a cylindrical gas-glass, having a bottom made of plaster-of-Paris. The solution of copper being in the tumbler, and the acid with the zinc in the gas-glass, the mould should be suspended by its conducting wire between the bottoms, the wire of the zinc connected with it, and the operation will proceed. In all cases it must be observed that the edge of the mould should be up, as, if it be placed horizontally, extraneous substances, sinking by their own weight, may be deposited upon it.

To produce a raised design upon a plate of copper, or as it is rather erroneously styled, “Engraving in Relief,” the operation is thus performed:—

The plate upon which the design is to be raised having had the conducting wire soldered to it, is covered with a coat of wax about one-eighth of an inch or less in thickness, and upon the surface of this coat the design is drawn. With a graver, the end of which must be of the form of a thin parallelogram, so as to make grooves in the wax equally broad at the bottom as at the top, the lines of the drawing are to be carefully cut down to the plate; care being taken that the plate is perfectly cleaned throughout each line, and also that the grooves are not narrower at the bottom than at the top. In order to lay the surface of the copper at the bottom of the grooves perfectly bare, the plate must be immersed in diluted nitric acid (three parts of water to one of acid), and the particles of wax that may have escaped the graver are driven off by the fumes of the acid. The plate is then placed in the apparatus, the circle closed as before, and the operation commences. As the particles of copper require a metallic base, they avoid the wax and seek the metal in the grooves; they there attach themselves to it, and to each other, until the hollows are quite filled up, when the plate is removed. If the surfaces of the ridges thus built up be not perfectly smooth, a piece of pumice stone or smooth flag, with water, being rubbed to them, will soon reduce them, after which the wax can be melted and cleaned off with spirits of turpentine; and so firm is this formation of metal thus raised, both in the adherence of its particles to each other and to the original plate, that it may be printed from at any ordinary printing-press.

One general remark applies to the production of electrotype copper, and it is, that the strength and solidity of the formation depends upon the slowness and deliberation of the process. The more slowly and deliberately the particles separate from the solution and proceed to their places, the more fitly they appear to take them up, and the more firmly they adhere; whilst on the contrary, if the operation be hurried, the metal is brittle, so much so as sometimes to powder under an ordinary pressure. The thicker and finer the partition of plaster between the two fluids, the more slightly are they connected, and consequently the slower is the circulation of the electricity. The proper length of time to be allowed for the process varies according to the nature of the work, and the strength or solidity required. Forty-eight hours seems to be the least time for forming a design in relief, and somewhat more than a week for a plate with sunk lines.

The laws which govern matter are mysterious. The entire of this process is so wonderful, that to descant upon it would be unnecessary; and, after all, it is but another step taken upon the path of science, each advance upon which, whilst disclosing new scenes and greater wonders, is only the needful preliminary to another which will display yet more!

N.