180 HISTORY OF PHOTOGRAPHY, 



quantity of water. By this immersion it should take a very fine blue 

 tint. If this is uniform, the paper is considered fit for the experi- 

 ment; in the contrary case it is sized again. It is then steeped in a 

 concentrated solution of bichromate of potash, and pressed between 

 folds of blotting paper and dried near the fire. To be eii'ective it 

 should be very dry. 



It is now fit for use. When the copy is effected, which requires in 

 sunshine about five minutes, the photograph is washed and dried. 

 When dry, it is steeped in a weak alcoholic solution of iodine, and 

 afterwards, when it has remained in it some time, it is washed in 

 water and carefully dried with blotting paper, but not at the fire, 

 for at a little below 100° F. the combination of iodine and starch 

 discolors. 



If it be considered that the drawing is not sufficiently distinct, this 

 immersion may be repeated* several times, for by this means may be 

 obtained the intensity of tone that is desired, which intensity can be 

 changed at will by employing a more concentrated solution of iodine. 



When the paper is damp the shades are of a very fine blue, but 

 Vv-hen it is dry the color becomes deep violet. If while the drawing is 

 still wet it be covered with a layer of gum arable the color of the 

 drawing is greatly preserved and more beautiful when it is dry. 

 When a paper is thus prepared it loses at first a little of its tone, but 

 it afterwards preserves its violet tint. 



THE CHROJMATYPE. 



This process, devised by the author, is a pleasing one in its re- 

 sults. It is exceedingly simple in its manipulatory details and pro- 

 duces very charming positive pictures by the first application. The 

 cliromatype is founded on the above process of Mr. Ponton's. One 

 dram of sulphate of copper is dissolved in an ounce of distilled 

 water to which is added half an ounce of a saturated solution of bi- 

 chromate of potash. This solution is applied to the surface of the 

 paper and when dry it is fit for use, and may be kept for any length 

 of time without spoiling. When exposed to sunshine the first change 

 is to a dull brown, and if checked in this stage of the process we get 

 a negative picture, but if the action of the light is continued the 

 browning gives way and we have a positive yellow picture on a white 

 ground. In either case if the paper when removed from the sun- 

 shine is washed over with a solution of nitrate of silver a very beau- 

 tiful positive picture results. In practice it will be found advanta- 

 geous to allow the bleaching action to go on to some extent. The pic- 

 ture resulting from this will be clearer and more defined than that 

 which is procured when the action is checked at the brown stage. To 

 fix these pictures it is necessary to remove the nitrate of silver, which 



