686 TRANSACTIONS OF THE 



In 1839 Talbot discovered the action of light upon the salts of 

 silver, and shortly after was successful in the preparation of pho- 

 tograjihic paper, on which he was able to fix designs. 



In 1841 he had so perfected the sensibility of paper, as to 

 enable him to obtain a patent, on what he called Calotype, which 

 has been changed to Talbotype; other processes on paper have 

 been called Energiatype, Chromotype, Authrotype, Amphi- 

 type, &c. 



France and England are now equalled by America in paper 

 Photography, and it is used for illustrating books, printing, &,c., 

 almost as successfully as upon metal plates. Chemical science 

 can make but little more improvement, except in the preparation 

 of material to work upon, and this will be chiefly paper, as glass 

 and other substances are apt to produce false shade and light. 



The selection of paper is of vast importance, particularly for 

 portraits; when selecting hold against a strong light, and choose 

 sheets free from iron stains, dust, or, in fact, any impurity, and 

 neither too much or two little glazed. Stop up with white wax 

 all the capillary punctures, so that it presents the appearance of 

 parchment, at the same time only filling the texture of the paper, 

 which the iodide of potassium most thoroughly penetrates and 

 also decomposes any greasy particles that may be in it, and if 

 when dry it presents a violet color, it is fit to take positive proof. 



When exposed in the camera an exact focus must be obtained, 

 and when the image appears distinct and clear in every part stop, 

 and depend upon your experience for the necessary time of ex- 

 posure to the light, recollecting that upon this depends the beauty 

 of your picture. You must know the temperature of the slate on 

 which you have the prepared paper, as well as that of the lens, 

 both of which should be equal, otherwise a vapor will prevent 

 the formation of a perfect image. White linen of some sort, being 

 a non conductor, should be placed over the camera, so that the 

 rays of light may be reflected without adding to the heat of the 

 box. The picture is develo])ed by a succeeding operation with 

 gallic acid, properly dissolved in distilled water. To fix the nega- 

 tive, plunge your proof into a hyposulphite bath, which will take 

 up the salts of silver without attacking the gallate of silver, upon 



