140 THE PRODUCTION OF POSITIVES, ETC. 



a rolling 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 suit- 

 able for amateurs than the process just described, 

 as the tedious washings between the application 

 of the different solutions is avoided, and the develop- 

 ment itself reduced to the simplest form by the use 

 of the ferrous oxalate process, employed for dry 

 plates. The results obtained by the employment of 

 Swan's opal plates, leave nothing to be desired as 

 far as artistic display and ornamental work is con- 

 cerned. Many of the most beautiful prints of poly- 

 cystinae 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 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 



