ELECTROTYPE. Besides the larger works produced by Electro•metallurgy, many exqui site copies of delicate works of art are pro duced by a modification of the same process, called .Electrotype.
Let the object to be copied be a small bas relief of about six inches by four, executed in a material such as marble, ivory, or plaster of Paris. A wax mould is made from the bas relief ; and this WAX is made a conductor of electricity by being brushed over with pow dered plumbago. The mould and a plate of copper are placed parallel, in a convenient vessel containing a solution of sulphate of copper. The copper plate must have a wire soldered to its upper edge, for the purpose of connecting it with that of the battery ; and the wax mould must be similarly connected with the zinc element of the battery. The mould and the copper plate being thus placed in the metal and connected by wires with the battery and the solution being poured in, the whole is left undisturbed from 2-4 to 36 hours ; at the end of which time, the mould, being de tached from the battery and withdrawn, will be found covered over with pure bright metal lic copper, rough on the miter surface ; but when separated from the wax by gently heat ing, it will, if the operation has been success ful, present a perfect copy of the bas-relief, every line of which, to the most delicate mark ings, will be found transferred to the metal with' more precision and delicacy than could have been produced by a cast made with the copper in a state of fusion. Perhaps few facts connected with the laws of aggregation of homo geneous matter are more striking than this, and few facts indirectly afford a more remarkable instance of the chemical divisibility of matter.
The copying of coins, medals, seals, and plaster casts, is extensively practised by the process above described. The production of copper busts, made entirely by deposition from solution, is also an example of the application of this process. Stig,lmayer;the sculptor, de vised a mode of coating colossal plaster statues with copper by the electro-process in the short space of two or three hours. Daguerreotype pictures are capable of being copied in electro type, by a kind of etching by galvanism ; and Mr. Smee has suggested the employment pf
a plan somewhat similar for etching in general.
The terms Electrotint and Gioltography have been applied to two methods of etching by electricity, in which the device is produced in rather a peculiar way. The methods are adapted, one for plate-printing, in which the design is in intaglio : and the other for sur face printing, as in common typography. Both have been partially brought into use, but not to any considerable extent.
A most curious instance of the extensive applicability of the art of electrotyping, is the fact of calico having been printed by means of it, The linen, steeped in proper liquids, is made to pass between rollers, one of which has patterns formed in it of different metals inserted into its substance, and connected with the zinc of a battery : the other roller is a simple metallic ponanctor: the current between fliee surfaces produces difibrent colours by the difference in their action on the common fluid, and thus the pattern is imparted to the calico.
The electrotype process has been recom mended not only for copying engravings, but for making the copper-plate itself on which an engraving is to he executed. The copper plates prepared for engravers generally con tain a small portion pf other metals, which render both the engraving and the etching somewhat uncertain. By the substitution, therefore, of plates produced by clectro-depo sition, in which the copper is quite unconta minated with other metals, an advantage is anticipated. To produce these plates, a cop per plate is prepared in the usual way and suspended in a copper solution, by which a film of any desired thickness maybe produced; and by a previous adjustment of the plate, the new portion may be separated from the old in the form of a distinbt plate, susceptible of after-preparation for the engraver. Or, the copper-plate, instead of being made by depo sition upon another plate of the same material, may be produced on a fiat surface of wax or plaster properly prepared.