Worthen, William Ezra, 1819-1897, [from old catalog] ed · New York, Appleton · leaf 70
e sunlight until thebackground is a metallic gray. The length of exposure may be from five min-utes up, depending on the intensity of the sunlight, the age of the preparedpaper, and the transparency of the tracing. Now lay the ferro-prussiate paperin the tray, cover with water, and leave it for… … Fig. 154. with a hinged backboard, to the inner side of which a piece of felt is glued inthe smaller sizes, while in the larger the felt is separate; on the back of thisboard are two brass springs fitting under the metal catch, making a close con-tact with the glass. As shown in the small seqtional…
Mechanical drawing
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