M. TECHNOLOGY. 517 



ium, or alum, and ten pounds of acetate of lead are to be 

 dissolved in the necessary quantity of warm water, and the 

 mixture allowed to stand until a deposit of sulphate of lead 

 has taken place. The clear liquid, which consists of acetate 

 of alumina, is to be poured off and mixed with five hundred 

 parts of water, in which dissolved isinglass is to be stirred. 

 The objects to be rendered water-proof are now to be im- 

 mersed in this mixture, and allowed to remain twelve hours, 

 until they become saturated ; they are then dried and fin- 

 ished. 6 (7, January 4, 1872, 8. 



NEW WOODBURY PHOTOGRAPHIC PROCESS. 



Woodbury, the author of the well-known photographic 

 process which bears his name, has devised a new mode of 

 printing, which begins by rubbing a glass plate with wax, 

 and then coating it with a thin layer of collodion. A solu- 

 tion of gelatine and bichromate of potash, containing a cer- 

 tain amount of finely pulverized glass, emery, etc., is then 

 poured on. After drying, this sheet is removed from the 

 glass and laid upon the negative, with the collodion side 

 downward, and then exposed to the light. After sufficient 

 illumination it is cemented by a solution of India-rubber to a 

 glass plate and washed with warm water, and after develop- 

 ment the relief picture is again removed from the glass plate. 

 The hydraulic press is next used to transfer this fine grain to 

 a plate of metal, the minutest detail of the dry image being 

 pressed into the soft metallic plate. A galvano-plastic coun- 

 ter-form is taken from this soft plate, and a cliche again taken 

 from this, which is immediately coated with steel or iridium. 



Another method of producing the relief granular picture 

 consists in preparing the different mixtures of chrome gela- 

 tine as above, differing only in the greater or less degree of 

 fineness of the granular substance. A sheet of thin paper is 

 allowed to swim upon the mixture which contains the coarsest 

 grains. After drying it is allowed to swim upon a second 

 mixture, with the medium-sized grains, and then again, after 

 drying, upon that with the finest. The gelatine sheet is now 

 illuminated under a negative, then fastened under water to a 

 finely polished steel plate, developed in warm water, and 

 dried. The image thus obtained is transferred to a soft me- 

 tallic plate, and a galvano-plastic copy taken. The finest 



