The stone should now be inked-in at once, because the turpentine, and with it all the fattiness, is liable to extensive evaporation, and then the stone will not take color well.
Inking-in of the pen designs is done as follows: A clean linen or woolen rag is soaked in clean water and wrung out till it is damp rather than wet. This is passed over the whole stone so that it becomes a little wet everywhere. Immediately after this dampening, the well-inked printing-roller is passed to and fro over the plate several times. The roller must be lifted frequently during this work so that the points of contact change. To lay the color on well and quickly, the roller should be held rather firmly in the beginning, well pressed down and used with a certain rubbing motion that will tend to lay color on the design sideways, so to speak. Then the roller must be allowed to roll to and fro a few times without much pressure, to spread the color and take away any surplus. Do not roll too long, till the stone dries, because then it will take dirt immediately. Should this occur, it must be wiped instantly with the damp cloth till it is clean again. If dirt is left too long, it will be extremely hard to remove.
Beginners usually wet their plates excessively to counteract this trouble of drying during the inking-in. This results in wiping away fine strokes, and the roller gets so wet that no good impression can be made till it has been dried sufficiently again. For this reason beginners should not use bath-sponge, because, though it is excellent, it leaves too much water on the stone unless one knows exactly how to use it.
Some printers put a little gum, others a little aquafortis into the water to wet the stone. Others use stale beer, or even urine. I consider all this unnecessary, if the stone has been prepared correctly and the color is good.
I have described the ink-rollers. I repeat that they must be uniform, soft, and elastic.
As to the inking-in color, I am not able yet to lay down a strict rule. All that I can say, as a result of my experiments and experiences, is:--
(1) The firmer the varnish in a color is, the cleaner is the work of inking-in.
(2) The same is true the more lampblack it contains.