386 Miscellanies. 



cess commences of changing the shadow upon the plate into a deep 

 engraving or etching. This is the decisive moment, and upon it must 

 be bestowed the greatest attention. The best method of proving if 

 the acid be strong enough, is to apply a drop of the acid in which the 

 plate now lies, to another plate : if the acid make no im.pression, it is, 

 of course, necessary to continue adding nitric acid; if, however, it 

 corrode too deeply, then it is necessary to add water, the acid being 

 too strong. The greatest attention must be bestowed upon this pro- 

 cess. If the acid has been too potent, a fermentation or white froth 

 will cover the whole picture, and thus not alone the surface of the 

 picture, but also the whole surface of the plate, will quickly be corro- 

 ded. When', by a proper strength of the etching powers of the acid, 

 a soft and expressive outline of the picture shall be produced, then 

 may we hope to finish the undertaking favorably. We have now 

 only to guard against an ill-measured division of the acid, and the 

 avoidance of a precipitate. To attain this end, I frequently lift the 

 plate out of the fluid, taking care that the etching power shall be di- 

 rected to whatever part of the plate it may have worked the least, and 

 seek to avoid the bubbles and precipitate, by a gentle movement of 

 the acid. 



In this manner, the process can be continued to the proper points 

 of strength and clearness of etching required upon the plates from 

 which it is proposed to print. I believe that a man of talent, who 

 might be interested with this art of etching, and who had acquired a 

 certain degree of dexterity in preparing for it, would very soon ar- 

 rive at the greatest clearness and perfection; and, from my experi- 

 ence, I consider that he would soon be able to simplify the whole pro- 

 cess. I have tried very often to omit the steaming and the gum ara- 

 ble, but the result was not satisfactory, or the picture very soon after 

 was entirely destroyed, so that I was compelled again to have recourse 

 to them. 



The task which I have undertaken is now fully performed, by 

 placing in the hands of the public my method of etching and print- 

 ing from the Daguerreotype plates, which information, being uni- 

 ted to the knowledge and mechanical experience we already possess, 

 and published to the world, may open a road to extensive improve- 

 ment in the arts and sciences. By thus laying open my statement to 

 the scientific world, I hope to prove my devotion to the arts and sci- 

 ences, which can end only with my life. — Atheneum, {London) May 23. 



10. Cloth of Glass. — Messrs. Williams and Sowerby of London, 

 have been exhibiting, at the Annual Show of the Polytechnic Institu- 

 tion, (London,) their process by which glass first spun by steam 



