46 ANNUAL OF SCIENTIFIC DISCOVERY. 



care, as certain precautions, very simple, but never to be overlooked, 

 are indispensable. Thus, contact with plaster, which contains a de- 

 structive salt, is to be avoided ; also, contact with iron, which is very 

 injurious, and liable to cause a rapid oxidation. Eave-gutters should 

 always be supported by galvanized brackets, and no gutter or sheet 

 zinc should be laid on oak boards." 



ON ETCHING. 



The London Builder furnishes the following practical notes on the 

 subject of " etching" with a view of especially commending the work 

 to amateurs in ornamentation. 



First, as regards copper plates, which in many respects have an 

 advantage over steel for the use of amateurs, procure a thin plate, 

 properly polished on the surface, at any of the regularly-established 

 coppersmiths. These can be had of the size of several feet down to 

 a few inches. The surface of the plate being bright and free from 

 tarnish, remove all grease with great care by washing with spirits 

 of turpentine and then rubbing with very fine whitening and wash- 

 leather. Care must be taken not to scratch the plate. 



Having got rid of all grease, fix a hand-vice to one corner or some 

 other convenient part of the plate ; it is then ready for the reception 

 of the etching-ground a preparation chiefly composed of asphaltum, 

 pitch, and virgin wax ; there is, however, a great art in making this 

 sufficiently plastic, so as to admit of its bein properly spread upon 

 the plate when heated. It is better, for ordinary purposes, to pur- 

 chase it at the coppersmith's or tool-shop, where a supply can be 

 had for about one shilling. A clabber, for the purpose of laying the 

 ground on the plate, is also necessary. This is of a mushroom shape, 

 and composed outwardly of very fine silk or kid leather, free from 

 grease ; the inside is padded with wool. This can be readily made 

 by any person who has seen one of them. In order to prevent any 

 grit or impurity which may chance to be in the etching-ground, it 

 is better to tie it in silk. For the purpose of heating the plate, a 

 hot iron, or a spirit lamp, placed below an iron frame on which the 

 plate may rest, or other contrivance, may be used. Care is to be 

 taken to make as little dust as possible. The metal must not be 

 allowed to get too hot, for that would burn the etching-ground, and 

 prevent it from sufficiently resisting the acid. The plate being of a 

 proper heat, by drawing the etching-ground over the face a small 

 quantity may be lodged upon it. This in the first instance is uneven ; 

 but may be spread in a flat, thin, even manner. Every part must be 

 covered by the ground, or else the acid would leave such places as 

 are bare liable to be corroded into holes. The ground, when this is 

 spread on the surface, is of a light brown color, so delicate that it is 

 difficult to see any pencil outline which might be transferred, or prop- 

 erly to see the scratches made by the etching-needle. In order to 

 darken this, it is necessary, while the plate and etching-ground are 

 still warm, to smoke it by the flame of a wax taper or candle. The 

 flame must be kept moving about, and not allowed to touch the plate 

 so closely as to burn the ground. 



These operations, although simple, require some little practice and 



