212 THE PHOTO-MICROGRAPHY OF 



not go too for. Then replace for a few moments in the hyposul- 

 phite solution, to dissolve out the new iodide of silver, before 

 giving the final washing. If under-developed, no intensifications per- 

 mitted by the dry-plate film will make up for it in this class of work. 



Collodion plates are to be preferred, since, in addition to the 

 possibility of making use of under-exposure and full development, 

 certain intensifying processes may be used which take away the 

 soft edge of the lines (caused by a slight halo around the edge of 

 the object), and thus sharpening the outlines greatly. The dry- 

 plate fihn does not permit of these processes being used ; hence, 

 in these the definition is not so good. 



If the window-glass of the room in wliich the exposure is made 

 is of a pretty deep orange colour, and the room long enough or so 

 arranged that one may work where there is not too much light, the 

 same room n.ay be used for developing collodion plates. In the 

 dark room an orange shade over the gas-jet gives a perfectly safe 



light. 



Plates are prepared by thoroughly cleansing them in nitric acid, 

 since with this former images are less likely to reappear than when 

 caustic alkali is used for cleansing. Then flow upon the concave 

 side the following solution of albumin : — Take the white of an egg 

 beaten a little, and dissolve it in twenty ounces of water ; add a 

 drop of strong ammonia. The plates are then set up in a rack to 

 dry, care being taken to shield them from dust, after which they 

 may be set away in the dark room on some convenient shelf to 

 keep clean until needed. If they are put in regular order, albu- 

 minised surfi^ce to the wall, it prevents confusion if one happens 

 to be in a liurry. The albumin coat is too thin to be visible, yet 

 it covers any little imperfection in the glass plate, and [n-events it 

 from appearing in the picture. It also makes the collodion flow 

 more smoothly. 



The usual medium negative collodion of the portrait photogra- 

 l^her has given me quite satisfactory results. It should be filtered 

 and then allowed to stand several hours, and decanted off the 

 deposit before using it. Occasionally, collodion used for line work 

 may be obtained. This works more slowly, but gives greater con- 

 trasts. \\'here it is desirable to make one's own collodion, the 

 following formula has been recommended to me : — 



