570 PHOTOGRAPHY 



perfect ease and convenience. The table is made to fold up when not in use ; and in 

 place of the ordinary dish for developing, a very efficient and portable tray is provided, 

 made of india-rubber cloth, having its two sides fixed and rigid, and its two ends 

 moveable ; it thus folds up into a space but little larger than one of its sides. The 

 working space of the table is economised thus : a portion of it is occupied in the 

 way just described : the silver-bath is suspended from the front of the table, and rests 

 upon a portion of the framework of the tent. This arrangement leaves ample space on 

 the table for manipulating the largest-sized plates. The collodion pourer, the plate- 

 developing holder, the developing cups, and the water-bottle, have all special points in 

 construction. The entire weight of the tent is 20 Ibs., and it is easily erected or taken 

 down by one person. Many improvements have been introduced in this tent, which 

 now render it nearly perfect. 



The processes of most importance may be divided as follow : 



1. The Copying process, already described. 



2. The Daguerreotype. See DAGUERREOTYPE. 



3. The Calotype. See CALOTYPE. 



4. The Collodion process, which must now be described 



THE COLLODN PROCESS. 



The difficulty with which we are met in any attempt to describe this photographic 

 process is t that it is almost hopeless to find two photographers who adopt precisely the 

 same order of manipulation ; and books almost without number have been published, 

 each one recommending some special system. 



By general consent the discovery of the collodion process, as now employed, is given 

 to the late Mr. Scott Archer. It will, therefore, be considered quite sufficient to give 

 the details of his process, which has really been but little improved on since its first 

 introduction. 



To prepare the collodion. Thirty grains of gun-cotton should be taken and placed 

 in 18 fluid ounces of rectified sulphuric ether, and then 2 ounces of alcohol should be 

 added, making thus 1 imperial pint of the solution. The cotton, if properly made, 

 will dissolve entirely ; but any small fibre which may be floating about should be 

 allowed to deposit, and the clear solution poured off. 



To iodise the collodion. Prepare a saturated solution of iodide of potassium in 

 alcohol say 1 ounce, and add to it as much iodide of silver, recently precipitated and 

 well washed, as it will take up : this solution is to be added to the collodion, the 

 quantity depending on the proportion of alcohol which has been used in the prepara- 

 tion of the collodion. 



Coating the plate. A plate of perfectly smooth glass, free from air-bubble or striae, 

 should be cleaned very perfectly with a few drops of ammonia on cotton, and then 

 wiped with a very clean cotton cloth. 



The plate must be held by the left hand perfectly horizontal, and then with the 

 right a sufficient quantity of iodised collodion should bo poured into the centre, so as 

 to diffuse itself equally over the surface. This should be done coolly and steadily, 

 allowing it to flow to each corner in succession, taking care that the edges are well 

 covered ; then gently tilt the plate, that the superfluous fluid may return to the bottle 

 from the opposite corner to that by which the plate is held. At this moment the plate 

 should be brought into a vertical position, when the diagonal lines caused by the fluid 

 running to the corner will fall one into the other, and give a clear flat surface. To 

 do this neatly and effectually some little practice is necessary, as in most things ; but 

 the operator should by no means hurry the operation, but do it systematically, at the 

 same time not being longer over it than is actually necessary, for collodion being an 

 ethereal compound evaporates rapidly. Many operators waste their collodion by 

 imagining it is necessary to perform this operation in great haste ; but such is not the 

 case, for an even coating can seldom be obtained if the fluid is poured on and off 

 again too rapidly; it is better to do it steadily, and submit to a small loss from evapo- 

 ration. If the collodion becomes too thick, thin it with the addition of a little fresh 

 and good ether. 



Exciting tlie plate. Previous to the last operation, it is necessary to have the bath 

 ready, which is made as follows : 



Nitrate of silver 30 grains. 



Distilled water 1 ounce. 



Dissolve and filter. 



The quantity of this fluid necessary to be made must depend upon the form of troiigk 

 to be used, whether horizontal or vertical, and also upon the size of tho plate. With 



