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



When the instrument is thus graduated, the focus may be set 

 in an instant (with an accuracy which is quite unattainable by 

 the unassisted eye), by merely measuring the distance of the 

 object if near, or by guessing at it if out of reach. 



13. To produce a calotype picture there are five distinct 

 processes, all of which, except the third (§25), must be per- 

 formed by candle-light; they are all very simple, but at the 

 same time all of them require care and attention. The first, 

 and not the least important, is 



14. The Iodizing of the Paper. — Much depends upon the 

 paper selected for the purpose; it must be of a compact and 

 uniform texture, smooth and transparent, and of not less than 

 medium thickness. The best I have met with is a fine satin 

 post paper, made by " R. Turner, Chaffbrd Mill." Having 

 selected a half sheet without flaw or water-mark, and free 

 from even the minutest black specks, the object is to spread 

 over its surface a perfectly uniform coating of the iodide of 

 silver, by the mutual decomposition of the two salts mentioned 

 in § 4. There is considerable latitude in the degree of dilu- 

 tion in which these salts may be used, and also in the manner 

 and order of their application ; but as the thickness and re- 

 gularity of the coating depend upon the strength of the so- 

 lution of nitrate of silver and upon the manner in which it is 

 applied, I think it ought by all means to be applied first, 

 before the surface of the paper is disturbed ; and I am in- 

 clined to believe, that if the solution be used of double the 

 strength suggested by Mr. Talbot, the coating will be found 

 more perfect and continuous, and will produce better pictures. 

 I use, accordingly, a solution of the strength of thirty grains 

 to the ounce of distilled water. 



15. The paper may be pinned by its two upper corners to 

 a clean dry board a little larger than itself; and, holding this 

 nearly upright in the left hand, and commencing at the top, 

 apply a wash of the nitrate of silver thoroughly, evenly and 

 smoothly with a large soft brush, taking care that every part of 

 the surface be thoroughly wetted, and that nothing remain 

 unabsorbed in the nature of free or running solution. Let the 

 paper now hang loose from the board into the air to dry, and 

 by using several boards time will be saved. 



16. The nitrate of silver spread upon the paper is now to 

 be saturated with iodine, by bringing it in contact with a so- 

 lution of the iodide of potassium ; the iodine goes to the silver 

 and the nitric acid to the potash. 



17. Take a solution of the iodide of potassium of the strength 

 of 200 grains to a pint of water, to which it is an improvement, 

 analogous to that of M. Claudet in the Daguerreotype, to add 



