An excess of ink is now well spread over the rollers and the plate is rolled in all directions. Close up all the middle tints and give the acid room only in the densest lights. This coating is done by warming the regularly covered plate to 31° C., and allowing the ink to flow down rapidly and cover the recesses. A second coating with slow manipulating of the rollers and manipulation of the handles without pressure, will yield a sufficient coat from above. If, despite this, certain parts should not be sufficiently blackened, rub on more ink till the covering is sufficient and the side protection perfect.
As in middle etching, we must proceed to the formation of an etching varnish by dusting with gums, placing into resin, by lightly rubbing this resin on in constantly renewed layers, till the absorptive power of the ink ceases; then warming and dusting warm with the same resin to complete saturation; then raising the heat as above, and dusting with asphaltum to saturation, heating stronger and finally placing the hot plate into asphaltum, which again secures all parts covered with ink and resin. {90}
At the different times of removing the dust, pay particular attention to the bright metallic parts. Over-removal of dust removes resin from the layer; under-removal leaves behind an obstinate yellow tint in the bright spots. Practice and experience readily prove the best teachers in this respect.
The final heating of the etching varnish must be pushed so far that an intimate connection is effected between all of its parts. This is easily noticeable from the uniform gloss of the mass. While still hot, the back of the plate is carefully varnished and cooling is promoted by dipping it into cold water.
Fig. 7.
But few spots are to be removed by chiselling (see Fig. 7), for the rollers have only blacked the middle of the highest lights. These spots, as indicated in middle etching, are scratched bright with a chisel. It is important always to scrape off the white edge around the drawing. Scratching of the plate does not even happen with beginners, except in cases of gross carelessness. If it does happen, a good covering with the turpentine solution of asphalt must be used. When this is all done properly we proceed to etch.
The process of etching by the aid of a brush is continued in periods of five minutes each. It is necessary to examine the side covering carefully at the end of every operation; a diligent brushing off of the surface is also to be recommended. Etching is continued until, by degrees, the lateral coating decreases and the grade grows narrower. At this juncture—that is, after about five to six operations (twenty-five minutes) the necessary depth is attained. In few cases (and almost always with beginners), it happens that a single coating does not suffice for deep etching without endangering the plate. In such cases wash the plate, coat it a second time, and form a second etching varnish.
When the depth is satisfactory the plate is washed and the new grade may be criticised.
After a proper examination, we proceed to the