PRACTICAL PHOTO-MICROGRAPHY, 125 



being sometimes added. The sensitiveness of the emulsion 

 varies in different makers' products, but it is usually consider- 

 ably higher than any collodion emulsion, and always lower 

 by a good deal than that of such gelatine bromide plates as are 

 used for the production of negatives. In order that the paper 

 may not curl and become unmanageable in aqueous solutions, 

 the gelatine film ought to be very thin ; and to counterbalance 

 its thinness it ought to contain a high proportion of the argentic 

 salts, otherwise vigor of image will be difficult to attain. 



The paper is placed face to face with a negative in a 

 frame in the usual way for contact printing, but this opera- 

 tion must be performed in non-actinic light, a simple yellow 

 glass not being sufficient protection against daylight, nor even 

 against ordinary artificial light. If there is any doubt as to 

 which is the face or gelatine side of the paper, it may be 

 laid down for a few moments on a flat surface, and it will 

 soon show signs of curling face inwards. Makers usually 

 send out three qualities of bromide paper : A Thin paper 

 with a surface glossy ; B Thicker paper with surface glossy ; 

 C Thick paper with a mat surface, which is not recommended 

 for our purpose. The sensitiveness does not appear to be 

 affected in any way by the surface, all grades being practically 

 alike sensitive. 



The development is usually effected by ferrous oxalate, tne 

 constituents being used in the proportions of from 4 to 6 parts 

 of the potassic oxalate to 1 part of the ferrous sulphate (see 

 page 63). We recommend the addition of at least one-half 

 a grain of soluble bromide to each ounce of developer. 



We have assumed a standard light and a standard distance 

 from light to printing frame. We now remark regarding 

 exposure : 



A dense negative requires long exposure, and vice versa. 



Long exposure tends to softness, detail, want of contrast. 



Short exposure tends to brilliance, contrast, pluck. 



Over-prolonged exposure leads, as a rule, to an unpleasant 

 color, a greenish tint, which is undesirable. 



Too short exposure leads to " chalk and soot," dense black 

 shadows, and glaring whites. 



