THE PRODUCTION OF POSITIVES, ETC. 141 



and allowed to dry spontaneously, a black backing is 

 attached. This produces that exquisite transparency 

 and softness so seldom seen since the Daguerreotype 

 process became extinct. 



For ordinary scientific work, however, the paper is 

 preferable, not only on account of its superior dis- 

 tinctness, but also because storage is facilitated by 

 its lightness, and its examination, by the absence of 

 any risk of fracture when handling it. 



Should it be desired to produce this paper at home, 

 it is only necessary to coat ordinary albumenised 

 paper with the emulsion described on a previous 

 page, as follows : — 



The melted emulsion is poured into a flat ebonite 

 tray, slightly larger than the sheet of paper to be 

 coated. The sheet being held at two opposite cor- 

 ners, so as to form a kind of angular spout, its most 

 central and lowest part is allowed to rest on the 

 emulsion, the ends at the same time being allowed 

 to sink gradually until the whole sheet rests evenly 

 on the surface of the emulsion. This gradual de- 

 scent prevents the possibility of any air bubbles re- 

 maining beneath the sheet. Should this however 

 happen, the end nearest the bubbles is raised and 

 again allowed to sink gradually, when it will be 

 found to push them before it in its descent. The 

 sheet is allowed to rest for a period varying from one 

 to ten minutes, according to the temperature of the 

 emulsion and finally hung up in the dark to dry. If 

 carefully guarded from actiuic light and damp, this 

 sensitised paper will keep indefinitely. 



