12 



desirable to have clear, and neglect the others. It is not advisable 

 to take new and old buildings in the same picture, as the time 

 necessary for the old will over-do the new. The sky is frequently 

 overdone, which may be prevented by interposing a black-screen 

 upon the glass over that part which corresponds to it, and which 

 may be previously ascertained by reference to the ground-glass. 

 Portraits should be taken in the open air, but not in the sun. The 

 best uniform back-ground is a blanket, but figures may be grouped 

 in front of a house, or a mass of foliage. There should not be 

 too much white in the dress, as it will be solarized or blotched, 

 before the other parts are distinctly pourtrayed. 



BRINGING OUT THE IMPRESSION. 



When the paper is removed from the frame, always in the dark, 

 nothing is visible ; it must then be again washed over with the 

 gallo-nitrate of silver, and exposed to a radiated heat from a gentle 

 fire, or a bottle of hot water,* or to what is still better, a jet of 

 steam, holding the paper vertically before it, never suffering the 

 paper to become in any part perfectly dry. When the picture is, 

 in the opinion of the operator, sufficiently distinct, it must be 

 carefully washed in distilled or rain water, as warm as the finger 

 can bear the water being changed once or twice, and then dried 

 in blotting-paper. 



FIXING PROCESS. 



To fix the picture, soak it for two or three minutes, or longer if 

 strongly developed, in a solution of half an ounce of hyposulphite 

 soda to a pint of water, turning it occasionally, and then soak it in 

 water from twelve to twenty-four hours, according to the thickness 

 of the paper, and dry it. The sweetness of the hyposulphite of 

 silver, which is readily communicated to any quantity of water, 

 affords an excellent means of testing when the picture is freed 

 from its influence. It should be washed until the water is per- 

 fectly tasteless. 



The Calotype process is intended solely tor the camera-obscura, 

 and the pictures so obtained are all negative ; that is, the lights 

 and shadows are reversed. From these, however, any number of 

 positive pictures, or pictures in which the lights are represented by 



* A convenient apparatus for this purpose may be had of Messrs. T. & R. Willats. 



