208 M. Niepce de Sainl-Victor on some 



maiiency. The latter application would be very advantageous 

 ibr the magic hiutern. 



The impressions may be obtained of various colours, such 

 as blue, violet and reii, according as the starch is more or less 

 boiled ; in the former case it inclines to red. A more or less 

 deep bistre colour is obtained liy exposing the impression to 

 the vapour of animonia ; but it accjuires its primitive colour 

 when varnished after this operation ; consequently an impres- 

 sion thus modified by ammonia cannot be varnisheil. 



I shall now speak of the imj)ressions which may be obtained 

 upon different metals. Thus, by exposing an engraving to 

 the vapour of iodine (for a few minutes only, so as to avoid 

 impregnating the white parts), subsequently laying it (without 

 wetting) upon a plate of silver and then placing it in a press, 

 in five or six minutes we have a most faithful copy of the en- 

 graving ; on subsequently exposing this j)late to the vapour 

 of mercury, we obtain an image resembling the Daguerreotype 

 imjiressions. 



Copper is operated upon as we have just stated for silver, 

 and tiie plate is subsequently exposed to the action of the 

 vapour of solution of anmionia, which is gently heated to pro- 

 duce a more copious disengagement; but care must be taken 

 not to expose the plate of copper until the first vapours have 

 escaped from the box, for this operation requires such an one 

 as is used for mercury. The same plate is subsequently 

 cleaned with water and a little tripoli. After this operation, 

 the image is developed and appears black like the preceding; 

 and moreover, the modification produced by the contact of 

 ammonia extends to such a depth in the plate, that it is not 

 obliterated until the metal itself is sensibly worn. 



The latter process will facilitate the labour of tool-engraving. 



The copying can also be effected on iron, lead, tin and 

 brass; but I know no means ot fixing the impressions. 



I shall only enumerate here, from among the n)any and new 

 experiments which 1 have made on iodine, those the results 

 of which are certain. Thus, 1 oiled an engraving printed with 

 printer's ink {encre g70sse), and when dry, exposed it to the 

 vapour of iodine. The impressions were analogous to the 

 preceding, except that they were less distinct. 1 subsequentl}' 

 made some sketches upon a sheet of white paper (sized with 

 starch) with black crayon, common ink (without gum) and 

 lead ; all were copied, and with still greater distinctness when 

 traced on paper prepared for oil-painting. I afterwards took 

 an oil-painting (unvarnished) and copied this also, with the 

 exception of certain colours composed of substances which do 

 not absorb the iodine. The sameapplies to coloured engravings. 



