Dr Fyfe on Baguerreotype. 209 



and thus all the variety of shades may be given, keeping [in 

 view that the silver surface always appears dark when in con- 

 trast -svith the mercurial one. 



That this is really the cause of the brilliant effects brought 

 out, is, in my opinion, proved by a very simple experiment. 

 If a plate, polished as for daguerreotype, with its highly re- 

 splendent surface, have an object placed on it — as a piece of pa- 

 per cut to any form, and moistened to make it adhere, and be 

 then exposed in the mercurializing box, the mercury being heat- 

 ed to the temperature recommended by Daguerre — those parts 

 exposed become mercurialized, while those covered with the 

 paper are not acted on. When the paper is removed, we have 

 a representation of the object, having all the appearance of a 

 daguerreotj-pe, excepting that it is merely in profile ; the sil- 

 ver "surface, or that representing the object, being dark, the 

 merculiarized surface being light. A similar result may be 

 obtained on other surfaces, as tin, tinned iron, and copper, 

 provided they be highly polished ; even on glass the same 

 effects may be produced, but in this last case it is necessary 

 to mercurialize at a higher temperature than for daguerreo- 

 type, and the plate, after being mercurialized, must be held in 

 a particular position, otherwise the object is not distinctly ob- 

 served. 



Dagueri'e has stated that, in Paris, the time that the plate 

 should be kept in the camera, during favourable weather, 

 should not exceed about three minutes ; and points out the 

 necessity of operating in the dark with the iodinized plate. 

 Though it may appear to some that there is no absolute neces- 

 sity for this precaution, I may mention, as corroborative of 

 what Daguerre has stated, that if an iodinized plate, with an 

 object placed on it, be exposed to direct sunshine, and instanlly 

 withdrawn, a distinct image will be found on it by mercurial- 

 izing and washing with hyposulphite. 



Daguerre has also remarked that, when inspecting the plate 

 during the mercurializing process, the light, even from a 

 candle, should not be allowed to flow long on it. However 

 improbable this may appear, yet it is not less true. The light 

 of a gas lamp affects it powerfully ; and hence, by exposing a 

 * plate to a gas flame, brilliant impressions can be procured. 1 



