Mr. Cundell on the practice of the Calotype Process. 331 



often described, and there are so many different modes of pro- 

 ceeding, that it may be sufficient to notice very briefly the best 

 process with which I am acquainted. Photography is in- 

 debted for it to Mr. Alfred Taylor, the eminent chemist, whose 

 pamphlet on the subject will supply every detail. His solution 

 is made by dissolving one part of nitrate of silver in twelve of di- 

 stilled water, and gradually adding strong liquid ammonia until 

 the precipitate at first produced is at length just re-dissolved. 



30. .Some paper is to be met with, containing traces of 

 bleaching chlorides, which does not require any previous pre- 

 paration ; but in general, it will be found necessary to prepare 

 the paper, by slightly impregnating it with a minute quantity 

 of common salt. This may be done by dipping it in a solu- 

 tion in which the salt can barely be tasted, or of the strength 

 of from thirty to forty grains to a pint of water. The paper, 

 after being pressed in clean blotting-paper, has merely to be 

 dried and smoothed, when it will be fit for use. 



31. The ammonio-nitrate of silver is applied to the paper 

 in the manner described in § 1 5 ; and when perfectly dry, the 

 negative picture to be copied is to be applied to it, with its 

 face in contact with the sensitive side. The back of the nega- 

 tive picture being uppermost, they are to be pressed into close 

 contact by means of a plate of glass; and, thus secured, they 

 are to be exposed to the light of the sun and sky. The ex- 

 posed parts of the sensitive paper will speedily change to lilac, 

 slate-blue, deepening towards black; and the light, gradually 

 penetrating through the semi-transparent negative picture, will 

 imprint upon the sensitive paper beneath a positive impression. 

 The negative picture, or matrix, being slightly tacked to the 

 sensitive paper by two mere particles of wafer, the progress of 

 the operation may from time to time be observed, and stop- 

 ped at the moment when the picture is finished. 



32. It ought then, as soon as possible, to be soaked in warm 

 water, and fixed in the manner described in § 27. 



33. In these pictures there is a curious and beautiful variety 

 in the tints of colour they will occasionally assume, varying 

 from a rich golden orange to purple and black. This effect 

 depends in a great degree upon the paper itself; but it is mo- 

 dified considerably by the strength of the hyposulphite, the 

 length of time exposed to it, by the capacity of the paper to 

 imbibe it, and partly, perhaps, by the nature of the light. 

 Warm sepia-coloured pictures may generally be obtained by 

 drying the paper, by pressure, and making it imbibe the hy- 

 posulphite supplied in liberal quantity. 



The paper of " I. Whatman, Turkey Mill," seems to give 

 pictures of the finest colour, and, upon the whole, to answer 



