PRACTICAL PHOTOMICROGRAPHY, 131 



The image in platinotype printing becomes under the action 

 of light visible ; with the Platinotype Company's original 

 process of image becomes rather faintly visible, with a new 

 process lately introduced from Germany, the image " prints 

 right out." "With the latter process, known as Pizzighelli's, 

 all that is required is to print the image to the required depth 

 and then to " clear" it with a weak dilution of hydrochloric 

 acid. The Company's ordinary paper is partly printed and 

 partly developed. 



For the Hot-bath Development process : The paper is ob- 

 tained from the company ready sensitized, it must be kept 

 away from light and perfectly dry. In order that it may be 

 kept quite dry it should be placed in a calcium tube, a light- 

 and-air-tight tube, having at one end a receptacle containing 

 calcic chloride in some shape. Sometimes the paper is bought 

 separately and the materials for sensitizing separately ; in such 

 cases full instructions accompany the goods. By means of 

 varying the proportions of certain ingredients of the sensitizer, 

 we may vary our results within limits or prepare a paper 

 more suitable than the ordinary commercial article to our 

 negatives. 



Every precaution must be taken with this paper to prevent 

 it getting damp in the least degree. A sheet of India-rubber 

 is put behind the paper and preferably overlapping it in the 

 printing frame. Printing is carried on till the shadows take a 

 very peculiar dirty green brown color, or until all the details 

 are faintly visible over the print, except, in a few cases, in the 

 very highest lights. After printing, the paper must again be 

 stored with every precaution against light and damp. Any 

 veil produced by light in this process is not, as in the albumen 

 process, removed by the after operations of toning and fixing, 

 for in platinotype there is no analogous " clearing " action. 

 Therefore the progress of printing must be examined in the 

 frame as rapidly as possible, and it may be noted that the 

 process of printing is much more rapid with platinotype than 

 with ordinary albumen paper. 



To develop platinotype prints. Make a saturated aqueous 

 solution of potassic oxalate at 60 degrees Fahr., and heat to 



