M. TECHNOLOGY. 493 



has stiffened, the frame is removed by the aid of a knife, and 

 the gelatine plate, with the adhering carbon print, is carefully 

 inverted. It is inked with printer's ink previously dissolved 

 in turpentine or benzole (without the addition of any varnish), 

 and distributed by means of a glass roller with a ground sur- 

 face. A sheet of uncoagulated albumen-paper is then laid upon 

 it, and, after being rubbed gently with a caoutchouc rubber, 

 is drawn from the plate. The paper must not remain too 

 long upon the plate, or it may soil the latter by solution of 

 some of the albumen. It is not necessary to dampen the 

 plate, since it is damp enough to yield several dozen impres- 

 sions, and when exhausted is so hygroscopic that it will again 

 absorb enough moisture from the air in a few hours. 15 C, 

 xxi., 331. 



IMPROVEMENT IN THE PREPARATION OF PLASTER CASTS. 



An improvement in the preparation of plaster casts of ob- 

 jects of art, etc., has lately been made by Mr. Caussinus, of 

 France, in what he calls the metallization of the plaster. 

 The details of this are at present a secret, although some hints 

 are given by a writer in a French journal. The cast is taken 

 in the ordinary manner, and when removed from the mould 

 is brittle and porous, as usual. It is then soaked in a fluid, 

 which the writer of the article referred to thinks is at the 

 same time both oily and silicious, and which imparts to the 

 cast a coating that enables it to resist a rather violent blow 

 without being injured, giving off at the same time a metallic 

 resonance. The pores of the plaster become filled, and the 

 whole substance is homogeneous and solid as stone. The 

 metallization consists in applying a salt of copper in a semi- 

 fluid condition, layer after layer being put on, and each pol- 

 ished before the application of the next coating. The total 

 thickness of the application is a fraction of a millimeter, and 

 it adheres with the utmost tenacity to the cast. Some sul- 

 phuret is then made to act on this coppery coating, so as to 

 bring about at once the effect of bronze; the form of the sul- 

 phuret, whether proto, deuto, or trito, corresponding with the 

 effect desired. The appearance of ivory, granite, porphyry, 

 colored marbles, or any other external condition, can be read- 

 ily given to the plaster. The result of the operation is said 

 to render the plaster as solid and homogeneous as metal it- 



