M. TECHNOLOGY. 485 



M. TECHNOLOGY 



FIXING DESIGNS ON GLASS. 



According to a process patented by E. Dode, the surface 

 of the glass is first finely ground, and any design then paint- 

 ed on it with a mixture of anhydrous boracic acid, gum, and 

 water. When dry, it is exposed to a temperature at which 

 the boracic acid fuses, and imparts to those portions of the 

 glass the usual lustre, and thus fixes the drawing. By mix- 

 ing various metallic oxides with the boracic acid, designs in 

 color may be produced. 15 (7, 1873, xxiv., 384. 



PHOTO-STEREOTYPING. 



It is stated by Fink that metal plates which can be em- 

 ployed in connection with ordinary type can be prepared 

 from photographic negatives, according to the following 

 simple process : A solution of 1 ounce of bichromate of pot- 

 ash in 15 ounces of water is slowly warmed, and 2 ounces of 

 fine gelatine gradually added. When the latter is complete- 

 ly dissolved, and the liquid has about reached its boiling- 

 point, it is filtered through fine linen. A piece of plate-glass, 

 several inches larger each way than the proposed picture, is 

 coated, in the dark, by pouring some of this solution on the 

 centre while the plate is in a horizontal position, distributing 

 the solution to the margin by means of a fine brush, and re- 

 peating the pouring until a film about one eighth of an inch 

 thick is formed. It is then allowed to drv, which will re- 

 quire two to three days, and is afterward exposed under a 

 transparent collodion positive, taken from a negative of the 

 object, to diffused light for ten to thirty minutes, and then 

 treated, in the dark, with lukewarm water in a tray, until 

 the relief is fully developed, which will be in from five to ten 

 minutes. After drying it with filter-paper, it is brushed with 

 glycerine with a fine, large, soft brush, the excess being re- 

 moved with filter-paper. A plaster matrix is formed from 

 this relief by pouring on it, while held in the hand, fine plas- 

 ter mixed with water to the consistency of oil, and tapping 

 it gently on the under side to remove air-bubbles, then 



