On a new Photo-Lithographic Process. 175 



subsequent soaking for a short time causes the unaltered 

 gelatine to swell in such a way as to raise the ink with it 

 from the paper, and a slight amount of friction, with a sponge 

 or other soft substance, removes the superfluous ink from all 

 parts of the inked print which correspond to the white parts 

 upon the original document. When the lines all appear 

 clear and well defined, boiling water is poured over the whole, 

 to remove the last traces of gelatine, and the print is dried. 

 We are now possessed of a bona-fide lithographic transfer 

 — that is a drawing in greasy ink of such a nature that it 

 admits of being transferred to the stone in the ordinary 

 manner, by simply inverting it thereon, and passing it through 

 the press ; the albumen, which will be found to have with- 

 stood all the washing, acting as the adhesive substance under 

 the ink to prevent the paper slipping on the stone. 



The whole of these operations need not occupy more than 

 from two to three hours- 

 Having now given a description of the leading features of 

 my process, allow me to offer a few critical remarks upon 

 those of others, having the same or similar ends in view, 

 prefacing them with some observations on the possible 

 means of obtaining the photo-lithographic image. 



While endeavouring to produce a delineation or drawing 

 upon lithographic stone, from which impressions can be 

 printed on paper in the lithographic press, it must be borne 

 in mind that the nature of such a delineation is what may 

 be styled ' c a reversed positive" — a positive, inasmuch as the 

 lines and shades are represented by similar lines and shades 

 upon the stone — and reversed, because those parts, which ou 

 the finished print appears on the right hand, are to the left 

 on the stone, and vice versa. Whatever means the operator 

 may adopt, his ultimate object is to produce a drawing of 

 this nature. 



In calling in the help of photography, the lithographer 

 will find that there are but three obvious ways in which the 

 agency of light can be used to aid him in producing a delinea- 

 tion upon a surface made sensitive to its chemical action. 



1st. The exposure of such a surface in the camera. 



2nd. Its exposure under a negative which has been made 

 in the camera ; or 



3rd. Its exposure under a positive, produced from such a 

 negative. 



Let us now examine the circumstances which attend the 

 application of each of these three methods in photo-litho- 



