26 



by the electrotype process, and when the coating begins to wear by 

 printing, it is removed by a weak acid, or by ammonia, which dis- 

 solves the ropper without affecting the silver under it. The plate 

 is coppered again, and after another printing the same operation is 

 repeated, so that a considerable number of copies may be printed 

 without much injury to the engraving. 



M. DAGUERRE'S NEW MODE OF PREPARING PLATES. 



The subjoined account of this process is taken from a letter of 

 M. Daguerre's to Mr. Arago, of the Academie, published in the 

 Comtes Rendus, No. 17, April 22nd, 1844. It presents many diffi- 

 culties, and has been adopted by very few persons in this country, 

 but as the latest contribution of the inventor of the Daguerreotype, 

 it deserves at least a fair trial. 



After stating that the proofs now obtained, though not deficient 

 in purity, leave much to be descried, in general effect and relief, 

 Monsieur Dagtierre continues thus : 



It is by superposing on the plate several metals, reducing! them 

 to powder by friction, and by acidulating the empty spaces which 

 the molecules leave, that I have been enabled to develop 'galvanic 

 actions which permit the employment of a much thickerSlayer of 

 iodide, without having to fear, during the operation of light in the 

 camera-obscura, the influence of the liberated iodine. 



The new combination which I employ, and which is composed 

 of several metallic oxides, has the advantage of giving a sensible 

 layer capable of receiving impressions simultaneously by all the 

 degrees of tone ; and I thus obtain, in a very short space of time, 

 the representation of objects vividly enlightened with demi-tints, 

 all of which retain, as in nature, their transparency and their 

 relative value. 



By adding cold to the metals which I first used, I am enabled 

 to avoid the great difficulty which the use of bromine, as an 

 accelerating substance, presented. It is known, that only very 

 experienced persons could employ bromine with success, and that 

 they were able to obtain the maximum of sensibility only by 

 chance, since it is impossible to determine this point very precisely, 

 and since immediately beyond it the bromine attacks the silver, 

 and is opposed to the formation of the image. 



AV ith my new means, the layer of iodine is always saturated 

 with bromine, since the plate may, without inconvenience, be left 



