170 THE FINE ARTS. 
Brockhaus, Leipsic) possesses a letter-engraving machine invented by C. 
Kretzschmar of Leipsic, which works admirably. 
2. Sreet-pLaTE Eneravine. The art of engraving on steel was invented 
by the English in the year 1820, and the principal credit of it is due to the 
copper-plate engraver Charles Heath; but it required British inventive 
genius and British perseverance to subdue that hard and brittle material to 
the operations of the graver and etching-needle. This art did not reach the 
Continent till some time later, and indeed in England itself it remained for 
a considerable time in the possession of individuals; but now steel-engray- 
ings are produced in France, Italy, and Germany equally as good as those 
of England. One part of the process, namely the etching-liquor, the 
English attempt still to keep a secret; but German ingenuity has long ago 
snipplied this deficiency, and the enti process is no secret now. 
The plates made use of in steel-engraving, or siderography, are of the 
finest English cast-steel with the stamp of Huntsman or Martial. Acier 
poule, or blistered steel, is also employed 1 in France and Switzerland. All 
this is steel of cementation, 2. e. it is produced in the cement-furnace by 
being subjected to a long suearod and powerful heat in a mixture of 
animal and vegetable substances and pounded glass; and it is better, 
harder, more brittle, more uniform, and more finely grained, and ean be 
more easily and uniformly hardened than the other sorts of steel. The 
plates, in order to guard against the warping to which they are liable in 
consequence of their cementation, are made somewhat thicker than copper 
plates. The cementation renders the plates, at least on the surface, quite 
soft; if they have become somewhat warped, they are straightened by 
hammering them with a wooden hammer on an anvil; they are then easily 
ground and polished. 
The ground and polished plate is thoroughly cleaned with spirits of tur- 
pentine, and is then coated with etching-ground in the same manner as a 
copper plate; but it must not be heated as strongly as the copper, for other- 
wise the ground will be apt to break up and form blisters, and even to 
evaporate. The etching-ground dissolved in spirits of turpentine may also 
be laid on with the brush, but always more thickly than on copper. When 
the outline of the drawing has been properly sketched or transferred, it is 
etched through precisely as in working on copper; but care must be taken 
that the needle actually scratches the surface of the plate, while the artist 
must be cautious not to breathe upon his work, lest it produce rust im the 
etchings, which will prove an obstacle to the subsequent biting in. The 
chief requisite now is a suitable menstruum or etching-liquor. Almost every 
engraver has a mixture of his own, which he naturally considers the best. 
We will here give only the one invented by Cooke in 1827, and which 
obtained the gold medal of Isis. When the plate is ready for biting in, 
mix and gently shake together six parts of acetic and one part of nitric 
acid, and pour this mixture upon the plate. As it acts very rapidly, it 
should not be left on the plate more than half a minute, at the expiration 
of which time the plate should be washed clean and dried with a gentle 
warmth or by blowing with the bellows. The light parts of the drawing 
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