152 THE PRODUCTION OF POSITIVES. 



press, or in its absence pressing them with a heavy 

 hot smoothing iron, a sheet of clean paper being 

 interposed between the surface of the iron and the 

 print. 



We strongly recommend the employment of a 

 professional photographer for the production of these 

 prints from ordinary negatives, as no amateur can 

 finish them off so well, without a useless expenditure 

 of time and money. 



An excellent method of producing glass or paper 

 positives by development, has lately been introduced 

 to the notice of photographers. It is more suitable 

 for amateurs than the process just described, as the 

 tedious washings between the application of the 

 different solutions is avoided, and the development 

 itself reduced to the simplest form by the use of the 

 ferrous oxalate process employed for dry plates. 

 Glass positives may be obtained by l.he employment of 

 Swan's opal plates which leave nothing to be desired 

 as far as artistic display and ornamental work are con- 

 cerned. Many of the most beautiful prints of polycy- 

 stinge, and diatoms especially coscinodisci we have 

 ever seen, were produced by this process. 



The simplicity of the manipulations and the direct 

 production of a positive by one process, is in itself a 

 recommendation to those who do not require a mul- 

 tiplication of proofs. All that is necessary after 

 exposure, development, and fixing in the ordinary 

 manner, is the application of a saturated solution of 

 bichloride of mercury, until the film becomes per- 

 fectly white. After the plate has been well washed 



