remarlaible Properties of Iodi?ie, Sfc. 207 



same engraving may be taken without subjecling it io th^ re- 

 newed preparatory process, and the last impressions are alw£iys 

 the most distinct ; for on leaving the engraving exposed for a 

 very considerable time to the vapour of the iodine, the white 

 parts ultimately become impregnated with it, if the paper has 

 been starched ; but the dark parts always predominate, how- 

 ever long the exposure may be continued. 



The engraving is in no way altered by the process, and it 

 may be copied an indefinite number of times. 



I have discovered a means of copying every kind of drawing 

 by the same process, whether made with printer's or common 

 ink (provided gum does not enter into its composition), or with 

 Indian ink or black-lead; in short, any kind of lined drawing 

 may be copied, but they must be previously subjected to the 

 following process: —they are first immersed for a few minutes 

 in a weak solution of ammonia, then in water acidulated with 

 sulphuric, nitric, or hydrochloric acid, and allowed to dry ; 

 they are then exposed to the vapour of iodine, and the process 

 above described repeated. By this method, tracings of de- 

 signs may be produced which hitherto could not be done in 

 any other wav, even when they existed in the substance of the 

 paper. Moreover, when there are two images, one on the 

 face and the other on the back of the same sheet of paper, 

 they can easily be copied separately. 



I have pointed out the necessity of the paper which is to 

 receive the impression of an engraving being sized with starch, 

 because the real colouring matter of the copy is the iodide of 

 starch; it afterwards occurred to me to coat the surface of 

 plates of porcelain, opaline glass, alabaster and ivory, with 

 starch-paste, and then to net upon them in the same manner 

 as I had acted upon the paper : the result, as I iiad anticipated, 

 was incontestably superior, as compared with the impressions 

 upon simple paper sized with starch. When the impression 

 obtained by this process is perfectly dry, it is coated with 

 picture-varnish; and when placed under glass, it acquires such 

 stability, that I have preserved some of them for more than 

 eight months without their undergoing any perceptible change. 



When I wish to copy an engraving, I prefer using opaline 

 glass, behind which I paste a sheet of paper to render it less 

 transparent: a reversed impression is obtained upon this plate; 

 but in using a plate of common glass which is subsecjuently 

 reversed, the proof appears non-inverted, and it is only requi- 

 feite to place a sheet of paper behind it to make the impression 

 more ap|)arent. It may also be kept as a window-pane ; but 

 in this case the impression must be placed between two plates 

 of glass, so as to preserve it from injury and secure its per- 



