Photographic Processes. 237 



Photography, with Textile, etc., Fabrics. Having been 

 brushed over with a moderately thick mixture of Spanish white 

 and alcohol, they are allowed to dry, after which they are care- 

 fully polished with cotton. Thus prepared, they may be 

 treated like positive paper, and will give as good pictures. 



Carbon Process. This has for its object a replacing of the 

 salts of silver by carbon in an impalpable powder, which is 

 imprisoned in a sensitive coating. It is founded on the fact 

 that the persalts of iron communicate to organic matter, such 

 as albumen, gelatine, or gum, an insolubility which ceases, un- 

 der the influence of light, in presence of tartaric acid. The 

 latter, in reducing the ferric compound, restores the natural 

 solubility of the organic substance, and allows both it and the 

 impalpable powder with which it has been combined to be 

 washed away, in proportion to the action of the light, so as to 

 reproduce on paper which has been coated with the mixture, 

 all the varieties of light and shade. Gelatine has been found 

 to answer best for the process. If only the under surface of 

 the coating is rendered soluble, the parts containing the middle 

 shades will be carried off in the washing, as well as those cor- 

 responding to the bright lights ; this is prevented, either by 

 causing the light to strike the outer surface first, or by modify- 

 ing the details of the process. The means of attaining these 

 objects have been well treated, in a paper read before the Pho- 

 tographic Society of Scotland, in December last, by Mr. Blair, 

 of Perth. The fixation of the picture is effected by removing 

 the ferruginous compound with acidulated water; and it is 

 rendered still more permanent by means of alum or corrosive 

 sublimate. The process has not yet produced results at all 

 comparable to those obtained with the salts of silver. 



The Ghrysotype. Paper is washed with a solution of ammo- 

 nia-citrate of iron, and dried. After exposure in the camera, 

 the faint image then perceived is brought out strongly by wash- 

 ing with a neutral solution of gold, and is fixed by means of 

 water acidulated with sulphuric acid, and subsequent treatment 

 with bromide, or, which is better, iodide of potassium. 



The Aurotype. Paper is washed with protocyanide of po- 

 tassium and gold, then dried. It will now darken very rapidly 

 when acted on by light, and the blackening continues in the 

 dark. Several combinations of gold and cyanogen may be used. 



The Platinotype. If a ferrocyanide of potassium and pla- 

 tina is formed, by mixing a boiling solution of chloride of 

 platina, which is as neutral as possible, with a saturated solu- 

 tion of cyanide of potassium, and paper is washed with it, 

 long continued exposure in a camera, during sunshine, will 

 cause a faint impression to be produced ; and washing with a 

 solution of proto-nitrate of mercury changes this into a delicate 



