PHOTOGRAPHY 571 



the vertical trough a glass dipper is provided, upon which the plate rests, preventing 

 the necessity of any handle or the fingers going into the liquid. If however, the glass 

 used is a little larger than required, this is not necessary. Having then obtained one 

 or other of these two, and filtered the liquid previously, the plate, free from any 

 particle of dust, &c., is to be immersed steadily and without hesitation ; for if a pause 

 should be made in any part, a line is sure to be formed, which will print in a subse- 

 quent part of the process. 



The plate being immersed in 'the solution must be kept there a sufficient time for 

 the liquid to act freely upon the surface, particularly if a negative picture is to be 

 obtained. As a general rule, it will take about two minutes, but this will vary with the 

 temperature of the air at the time of operating, and the condition of the collodion. In 

 cold weather, or indeed anything below 50 Fahr. the bath should be placed in a 

 warm situation, or a proper decomposition is not obtained undefc, a very long time. 

 Above 60 the plate will be certain to have obtained its maximum of sensibility by 

 two minutes' immersion, but below this temperature it is better to give a little extra 

 time. 



To facilitate the action, let the temperature be what it may, the plate must be lifted 

 out of the liquid two or three times, which also assists in getting rid of the ether from 

 the surface, for unless this is thoroughly done a uniform coating cannot be obtained ; 

 but on no account should it be removed until the plate has been immersed about half a 

 minute, as marks are apt to be produced if removed sooner. 



The plate is now ready to receive its impression in the camera obscura. This having 

 been done, the picture is to be developed. 



The development of the image. To effect this the plate must be taken again into the 

 dark room, and with care removed from the slide to the levelling stand. 



It will be well to caution the operator respecting the removal of the plate. Glass, 

 as before observed, is a bad conductor of heat ; therefore, if in taking it out we allow 

 it to rest on the fingers at any one spot too long, that portion will be warmed through 

 to the face, and as this is not done until the developing solution is ready to go over, 

 the action will be more energetic at those parts than at others, and consequently destroy 

 the evenness of the picture. We should, therefore, handle the plate with care, as if it 

 already possessed too much heat to be comfortable to the fingers, and that we must 

 therefore get it on the stand as soon as possible. 



Having then got it there, we must next cover the face with the developing solution. 



This should be made as follows : 



Pyrogallic acid ...... 5 grains. 



Glacial acetic acid 40 minims. 



Distilled water 10 ounces. 



Dissolve and filter. 

 Mr. Delamotte employs 



Pyrogallic acid 9 grains. 



Glacial acetic acid ...... 2 drachms. 



Distilled water ... . . 3 ounces. 



. Now, in developing a plate, the quantity of liquid taken must be in proportion to its 

 size. A plate measuring 5 inches by 4 will require half an ounce ; less may be used, 

 but it is at the risk of stains ; therefore we would recommend that half an ounce of 

 the above be measured out, into a perfectly clean measure, and to this from 8 to 12 

 drops of a 50-grain solution of nitrate of silver be added. 



Pour this quickly over the surface, taking care not to hold the measure too high, 

 and not to pour all on one spot, but having taken the measure properly in the fingers, 

 begin at one end, and carry the hand forward ; immediately blow upon the face of the 

 plate, which has the effect not only of diffusing it over the surface, but causes the 

 solution to combine more equally with the damp surface of the plate ; it also has the 

 effect of keeping any deposit that may form in motion, which if allowed to settle, 

 causes the picture to come out mottled. A piece of white paper may now be held 

 under the plate, to observe the development of the picture : if the light of the room is 

 adapted for viewing it in this manner, well ; if not, a light must be held below, but in 

 either case arrangements should be made to view the plate easily whilst under the 

 operation : a successful result depending so much upon obtaining sufficient develop- 

 ment without carrying it too far. 



As soon as the necessary development has been obtained, the liquid must be poured 

 off, and the surface washed with a little water, which is easily done by holding the 

 plate over a dish, and pouring water on it ; taking care, both in this and a subsequent 

 part of the process, to hold the plate horizontally, and not vertically, so as to prevent 

 the coating being torn by the force and weight of water. 



