PHOTOGRAPHIC E.NGBAVi.NO.] UNDULATORY FORCES. LI G HT PHOTOGRAP H Y. 



161 



PHOTOGRAPHIC ENGRAVING. 



THE usual process of copying from negatives is necessa- 

 rily somewhat slow, and therefore greatly limits the 

 production of paper positives. A great variety of at- 

 tempts has accordingly been made, the object of which 

 has been to produce blocks, on which photographic pic- 

 tures could be engraved, and printed from. 



Some of the earliest experiments for this purpose were 

 made on Daguerreotype plates. These were etched out 

 by chemical means, or electrotyped, so as to present an 

 uneven surface, which would afford the effects of light 

 and shade when engraved from. 



One of the best prints which was made by this pro- 

 cess, was produced many years ago, by Mr. Grove, at 

 " the London Institution ; being an outline of that build- 

 ing, obtained from a Daguerreotype. However, no 

 great success attended the efforts then made. 



Mr. Fox Talbot and others have, since then, made 

 considerable advance in this department of photographic 

 practice. Pictures have been transferred to stone and 

 wood ; and, from these, engravings have been produced. 

 We shall confine our remarks to two processes ; the first 

 being that of photozincography, for an account of which 

 we are indebted to the Plu>tnyraphic Newt Almanac ; 

 and M. Pretcsh's prdcess, which the inventor kindly ex- 

 plained to us himself, and the whole of which we have 

 frequently repeated. 



hotoziucographic process is described as follows: 



"The most successful method of carbon printing, is 

 that perfected by Colonel Sir Henry James, R.E., 

 Director of the Ordnance Survey of Great Britain ; which 

 has led to the most important results, both in an artistic 

 and economical point of view. The singular advantage 

 which this art possesses, consists in the fact, that we 

 can now produce authentic copies of any of the numerous 

 rare manuscripts, which are carefully preserved in dif- 

 ferent parts of the world; and print any number of 

 copies of them that may be required, at a cost which 

 will not exceed one penny for a folio sheet, and this 

 without ever touching the original document ; or, if 

 n -'I, without even being in the same room with it, 

 )iriiviili-.l we have a hole in the wall, to place the lens of 

 tin: (.anu-ra in. 



" Photozincography is the name given to this process, 

 which is the art of producing a photographic foe simile 

 of any subject ; such as a manuscript, a map, a line 

 engraving, and transferring the photograph to a zinc 

 plat<' ; thereby obtaining the power of multiplying copies 

 iu the same manner as is done from a drawing on a 

 lithographic stone, or on a zinc plate. 



"The process is based on that first suggested by 

 M. Aser, of Amsterdam ; viz. , the obtaining a photo- 

 graphic picture on paper prepared with the bichromate 

 of potass ; washing off the unchanged salt ; inking the 

 image left on the paper with photographic ink ; and then 

 transferring the same to a prepared zinc plate, from 

 which any number of impressions may be printed. 



" Tho steps to be taken to obtain this important result, 

 are first, to produce a collodion negative on glass, in the 

 usual manner, of the document to be copied ; this nega- 

 tive may be identical in size with the original, or larger 

 or smaller, as may be most desirable. The greatest care 

 is required in obtaining this negative perfect, as any 

 ts it may contain, will necessarily be reproduced in 

 the copies. The lenses employed must be in due relation 

 with the size of the object copied, so as to avoid distortion. 



"The negative will require to be intensified, in order 

 th.it whiteness of the paper may be reproduced in the 

 l"nitive. This intensity is readily obtained by immers- 

 ing the fixed negative in a saturated solution of bichlo- 

 ride of mercury, washing it with water, and then putting 

 it into a solution of commercial hydrosulphate of ammo- 

 nia ; one part to ten parts of water. 



" In tlii.n manner the ground of the negative is 

 lured extremely dense, without the clearness of tho 

 details being in the least affected. When dried and 

 varnished it is ready for use. 



i 

 i ,, 



3 -, ounces. 



"With this negative we proceed to obtain positives 

 on paper. The quality of this paper is a point of much 

 importance ; the best is that known as ' engravers' 

 tracing-paper. ' 



" A solution of gum-arabic is made by dissolving three 

 ounces of the gum in four ounces of water. 



" Roiling water is saturated with bichromate of potass ; 

 and two parts of the solution is mixed with one part of 

 the gum-water, both being kept at a temperature of 

 200 Fah. 



" The tracing-paper is evenly coated with the hot 

 mixture, by means of a flat camel-hair brush, and dried ; 

 it is then exposed to light, under the negative, in the usual 

 way. The time for printing may vary from two minutes 

 in the sunshine, to ten minutes in clear diffused light. 

 If a good image is not obtained in that length of time, 

 the operation had better be deferred to a more favour- 

 able opportunity. The period of exposure is determined 

 by the appearance of the print ; when all the details 

 have become distinctly impressed, it may be removed. 



"The next thing is to coat the eutire surface of the 

 print with an even and thin layer of a greasy ink, which 

 may be composed of the following ingredients : 



" Middle linseed oil varnish . 4j ounces. 



Wax 



Tallow .... 

 Venice turpentine 

 Mastic resin 

 Lampblack 



"A portion of these is dissolved in turpentine suffi- 

 cient to form a tlu'n cream, which is applied to tho 

 surface of the positive print with a brush. 



" The turpentine is allowed to evaporate for half-an- 

 hour, and the positive is then floated, face upwards, on 

 hot water for a few minutes ; then removed, and laid, in 

 the same position, on a porcelain slab. 



"The surface is then gently rubbed with a sponge, 

 dipped in warm gum-water, when the ink readily 

 leaves the surface at those parts which have been un- 

 acted on by light ; while it adheres tenaciously to the 

 details of the image. 



"As soon as the lines are quite clear, the print is 

 placed on a flat dish, and washed, first with warm, and 

 finally with cold water. When dry, it is ready for 

 transferring to zinc or stone. 



" There are two methods of transferring to zinc, vary- 

 ing according to the quantity of ink in the photograph. 



"If a very small quantity has been applied on ac- 

 count of the closeness of the lines in the subject, the 

 print is transferred by tho antistatic process. 



" If a larger quantity of ink has been applied, the pro- 

 cess is different 



"The positive is laid for ten minutes between sheets 

 of paper, damped as uniformly as possible with water ; 

 it is then laid face downwards on the plate, covered with 

 two or three sheets of paper, and passed once through 

 an ordinary lithographic press. The sheets of paper 

 being removed, it is damped at the back with gum- 

 water, till its adhesion to the plate is so lessened that it 

 can easily be pulled off. After tho transfer has been 

 gummed, brought up, and etched, the ink is cleared off 

 with turpentine, and the design is rolled up with print- 

 ing-ink. Impressions can then be taken from it. 



" The quantity of ink necessary to be applied to a 

 photographic positive, to make a successful transfer to 

 grained zinc, is greater than that which is necessary 

 for stone; and the anastatic process requires the least 

 of all. 



"The action of the warm water in which the positive 

 is immersed on the insoluble gum, is to cause it to 

 swell ; and the ink which overlies the lines formed of 

 insoluble gum, expands likewise. It is evident, there- 

 fore, that if the subject photographed be of a close 

 nature as a fine engraving the amount of enlargement 

 of the inked lines may be sufficient to bring them into 

 contact while tho print is in tho water ; and when they 

 have once coalesced, they will not separate again when 

 the gum shrinks in drying, and there will consequently 

 be a continuous shade of ink instead of lines. In such 



