July, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



149 



Electrotyping. 



By Dr. F. Mollwo Perkin. 



In the article on electrotyping in the January number 

 of " Knowledge " various methods for reproducing 

 medallions, coins, &c., were given. But this does not 

 by any means exhaust the possibilities of electrolytic 

 reproduction. Statuettes, and even large statues, can 

 be, and often are, copied in a similar manner. Thus 

 a statue of the Earl of Eglinton, which is 13 J feet 

 high, was reproduced by Messrs. Elkington and Co., 

 the weight of the electrolytic copper being about two 

 tons. The reproduction of a statue, as may readily be 

 imagined, is not by any means an easy or simple pro- 

 ceeding. 



Generally speaking, the original is first formed in 

 plaster of Paris. The plaster cast is then thoroughly 

 saturated with boiled linseed oil or with melted paraffin 

 wax. After standing for some time to allow the oil 

 or wax to thoroughly set and harden, the entire surface 

 is brushed over with graphite, and is then polished, so 

 as to form a homogeneous conducting surface. 



The model so prepared has conducting wires fixed 

 against different portions of the surface, so that the 

 electric current may be evenly distributed, and is then 

 connected with the negative pole of the source of 

 current and placed in a copper sulphate bath. When 

 a coating of sufficient thickness has been obtained— 

 about i: or more of an inch — the figure is removed from 

 the bath and carefully washed. It is now necessary 

 to remove the plaster form, and this is done bv cutting 

 the deposited copper in appropriate parts, so that the 

 copper shell can be removed in portions. The fewer 

 cuts that require to be made, the better, so that the 

 portions of shell may be as large as possible. 



The parts or " formes " of the copper shell so ob- 

 tained represent the negatives or moulds upon which 

 the positive is to be deposited. The inner portion of 

 the formes are exposed to the fumes of sulphuretted 

 hydrogen or are washed with a dilute solution of 

 potassium sulphide. By this means the copper becomes 

 coated with a thin film of copper sulphide, which is 

 conducting, but upon which the copper to be deposited 

 will not adhere. The outer surfaces of the mould are 

 varnished to render them non-conducting. The vari- 

 ous portions of the shell are then placed in a coppering 

 bath and the current passed. When the deposited 

 copper reaches a thickness of about J of an inch, thev 

 are removed from the bath and well washed. The 

 freshly-deposited shell is now carefully stripped off 

 from the outer shell and the different parts joined to- 

 gether. 



Stereotyping. — The most important application of 

 electrotyping is in the preparation of stereotypes. 

 When a large number of copies of a book require to 

 be run off, and in order not to keep too large a quantity 

 of type set up, a copy is reproduced in stereotype. 

 The following description of the procedure adopted is 

 the principle of the process, although individual firms 

 adopt methods which vary in detail. Suppose it is re- 

 quired to produce a stereotype of a page of a book. 

 The set-up type is placed face downwards upon a wax 

 plate (gutta compositions are very often employed) 

 cast upon a sheet of lead. It is then placed under an 

 hydraulic press, by which means a perfect impression of 

 the type is obtained in the wax. The type is then re- 

 moved from the wax impression, which is then 



graphited, being generally first slightly warmed to 

 render it just soft, so that it takes the graphite more 

 thoroughly. Of course, it must not be sufficiently 

 heated to blur the sharp edge of the impression. 

 Pieces of stout brass wire are now pushed through the 

 wax imtil they come in contact with the graphite at 

 variou.^ parts where they will not injure the impression 

 of the type. These pieces of wire are to make electrical 

 contact so that when the current is passed it may be 

 evenly distributed. 



The prepared impression is now placed in the copper- 

 ing bath and subjected to a fairly low current until the 

 whole of it has obtained a complete coating of copper. 

 It is now either left in this bath until a sufficiently thick 

 shell has been produced or else it is taken out and 

 placed in the quick-depositing bath, where a much 

 higher current density is employed and the electrolyte 

 is kept well agitated by blowing air through it. In the 

 quick bath the shell may be finished in an hour or two, 

 but may take a day or two in the slower bath (some- 

 times it is placed directly in the quick bath without 

 being first treated in the slower one). As soon as a 

 sufficiently thick deposit of copper has been obtained, it 

 is removed from the bath, and if the stereo is small the 

 wax is stripped away by hand. But in cases where the 

 shell is of any considerable size, and, therefore, liable 

 to be damaged, the wax is usually melted out with hot 

 water or by blowing on steam. The galvano is now 

 thoroughly cleansed from adhering wax and graphite 

 by brushing it in hot water and with caustic soda or 

 dilute hydrochloric acid. The next process is to back 

 up the copper, because as the shell is less than one 

 millimetre thick it is much too thin and fragile to use 

 ff)r printing purposes. But before the backing up 

 metal, which usually consists of lead containing about 

 6 per cent, of antimony to harden it, is poured in, the 

 shell must be tinned, otherwise the lead will not adhere. 

 A very satisfactory way to do this is to first brush the 

 inside of the shell with some soldering fluid, then place 

 the shell face downwards upon a flat iron plate and 

 float the iron plate upon a bath of molten metal slightly 

 hotter than the melting point of tin. As soon as the 

 copper shell has become properly heated, powdered tin 

 is sifted over it, care being taken to give it a perfectly 

 homogeneous coat. The tin melts and alloys with the 

 copper, and now the lead can be poured in and it in 

 turn alloys with the tin. After cooling and machining 

 the edges and planing off the excess of lead, the stereo 

 is ready for use. 



Facing stereotypes. — When the copper stereo has been 

 used for some time, owing to the copper being a soft 

 metal, there is a tendency for the sharpness of the im- 

 pression to become blurred; furthermore, certain print- 

 ing inks, such, e.g., as red ink, which contains Ver- 

 million — sulphide of mercury — act upon the copper and 

 unite with it. In order to get over these difficulties 

 the stereotypes are very often " steel " or nickel faced. 

 The term steel facing is not quite correct, but it has 

 been the custom to call iron when electrolytically de- 

 posited steel, because, although its hardness is not due 

 to its carbon contents, yet it has very much the pro- 

 perties of steel. It is more usual to employ iron as a 

 facing rather than nickel, because when used for a 

 considerable time even iron and nickel facings wear off. 

 It is then necessary to reface, but before this can be 

 done it is essential that all of the original facing should 

 be removed. The iron facing is very readily removed 

 with dilute sulphuric acid, which has practically no 

 action on the copper, but nickel is extremely difficult to 



