. The book of photography; practical, theoretical and applied. e glass in a solution of aurantiauntil the desired effect is obtained. Allowto dry thoroughly, cut round the edges,and strip off the glass. Collodion may beused instead of gelatine, in the samemanner. Some workers prefer to add thedye to the gelatine solution or collodionbefore applying to the glass. Sucha screen should be a pale lemon yellow,and of sufficient depth to increase the ex-posure by three times. It will be suitable for use in ordinarj^ landscape work whennecessary, where all that is required is tocut out the ultra-viole
. The book of photography; practical, theoretical and applied. e glass in a solution of aurantiauntil the desired effect is obtained. Allowto dry thoroughly, cut round the edges,and strip off the glass. Collodion may beused instead of gelatine, in the samemanner. Some workers prefer to add thedye to the gelatine solution or collodionbefore applying to the glass. Sucha screen should be a pale lemon yellow,and of sufficient depth to increase the ex-posure by three times. It will be suitable for use in ordinarj^ landscape work whennecessary, where all that is required is tocut out the ultra-violet and slightly tonedown the blue. Matching the Screen to the Plate. It is often necessary to bring into playboth the influences previously referred to,namely, to use not only the speciallysensitive plate, but a suitable screen Bausch and Lomb Ray Filter () is a very convenient arrangement forsecuring a colour screen of any desiredtint or depth. It consists of two thinpieces of optically worked glass betweenwhich is cemented a glass ring, thus. Fig. 595.—Bausch A^•D Lome Filter. forming a cell into which any suitablesolution may be introduced through asmall opening by means of a pipette. Theglass portion is mounted in a metal ringwith screws for attaching to the speaking, a very pale screenis sufficient, and it is safer always toemploy one of this character. It mustbe understood, however, that the depthof the screen is dependent upon (a) thecharacter of the subject, or its combina-tion of colours, and (b) the special sensi-tiveness of the plate. It will be necessary,therefore, to make a few experiments witha view to finding the exact depth of tintrequired to produce a certain effect witha certain plate. ORTHOCHROMATIC PHOTOGRAPHY. u: Making a Graduated Screen. Take an ordinal} dry plate, immerseit in a 1 per cent, solution of potassiumbichromate, and dry it in the dark in agood current of air. (The same precau-tions must be taken in drying
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