The second rag with the lighter color must not be filled with it in mass, but should merely be made sooty with it, so to speak. Otherwise the lighter color would penetrate the deeper lines also and mix there with the heavier color.
In the end the stone must be wiped again with an entirely clean rag, as will be understood, of course, and thoroughly cleansed of all the color.
II
THE ETCHED METHOD
In this the design is not engraved into the stone by pressure of the hand, but with aquafortis or other acid, and only so much pressure is exerted in making the design as is required to cut through the thin coating of varnish with which the stone is covered. Therefore this method permits great freedom of action and is applicable especially for landscape work and for drawings in Rembrandt's style. In treatment as in effect it resembles copper plate, and has its own advantage in that the lines may be strengthened gradually by stronger pressure on the engraving-needle. They may even be engraved a little into the stone so that afterward the lines will become stronger under etching. This cannot be done with copper at all or only with great difficulty.
These considerations and the quicker printing permitted by it recommend the method to artists. In other respects it is not different from working on copper. But it is necessary that a good lithographer should be a master of this form of stone work, as it may be used for excellent work, not only by itself but in combination with the other methods.
The stone must be ground as smoothly as possible, then treated with aquafortis and coated with gum, so that its surface thus is completely prepared. The aquafortis may be as strong as that used for etching pen work. It suffices, also, to wipe the plate merely with a sponge dipped in stronger aquafortis, the chief point being that no roughnesses shall be caused by uneven etching.
A few minutes after this first operation is finished, the stone is rinsed with water, dried and coated with etching-ground. This can be best done as follows:—
(1) Warm the stone till an ordinary copper etcher's etching-ground will become so fluid on it that it can be worked with a leather ball like a varnish, and can be spread very thin and very evenly. Great care must be exercised lest uneven warming crack the stone. If one can put it into a nearby baker's oven, it will obviate the necessity for an especial apparatus, which otherwise is demanded.
After coating the stone with the etching-ground, it is reversed while still warm, and blackened by applying the flame of a tallow or wax candle, as the copper-plate etchers do with their plates. Then the stone is set aside to cool, with great precautions against dust. After it is cool, dust will not harm it, and it can be kept indefinitely before use, so long as the coating is protected against injury.