Now we come to an important matter, namely, the correction of errors. It does not happen often that a drawing or inscription can be made entirely without error, and it would be a great imperfection in lithography if these mistakes could not be corrected at once.
Errors may be observed before etching or afterward. Different ways of making corrections are required.
It is very easy to make corrections before etching. If the error is observed as soon as it is made, while the ink still is wet, it may be corrected by merely wiping out the defect with the finger. If the ink is dry, oil of turpentine is required. In each case the ink must be well removed so that it will not resist the etching fluid later. If only tiny spots are defective they can be corrected by delicate use of a sharp eraser. Defects that need merely to be destroyed without drawing anything else in their place may be scraped off with a knife or with pumice stone.
After the plate is etched, errors demand treatments that differ according to whether a defect or blemish is merely to be removed, whether something else is to be drawn in place of the removed part, or if something has been forgotten and is to be added. The area of the correction also makes a difference.
If it is only a matter of removing small defects or places, delicate erasure will do. The same, or polishing with pumice, is done if the area is larger. Then the corrected spots must be coated with a mixture of gum and aquafortis, using a soft brush very carefully that it may not touch any of the sound places.
If something new is to be drawn in, the process is different. Ink-in the stone very clean, and coat it with gum and water that is very thin and delicate. Let it dry. Then scrape the defective places away very carefully or grind them away by rubbing with pumice stone. Coat the spots cautiously with soap-water or oil of turpentine and clean off again as thoroughly as possible. (This coating is not necessary in the case of a few isolated small lines or points.) Now draw in your new design with chemical ink, and as soon as this is dry, etch the corrections carefully with a small brush and then prepare with gum.
The third case, where something has been forgotten, is treated almost the same way. If it is only a very small thing, the stone need merely be scraped carefully. Then the drawing may be put in, preferably with a thicker ink. If the area is large, the stone must be ground where the design is to be added, coated with soap-water or oil of turpentine, and then treated as explained before.
When the stone has been corrected and prepared for printing, it can be used at once or set aside for some length of time. In the latter case it should be inked with a firm color and coated delicately with gum solution. Then it can be held as long as desired. Coating with gum solution is advisable not merely for storing away, but for every interruption of printing that lasts more than five minutes.
If a stone has stood longer than a day without being freshly inked, it must be wiped off first of all with gum solution and oil of turpentine, that it may take the color well, so that the very first impression may be perfect. During the progress of printing, the following points are important: Uniform distribution of water, the same of printing-color, frequent inking of the inking-roller, and the very greatest speed possible.
In the main points the brush process is like that of the pen. The chief difference is that it is not possible to make the brush strokes as strong as those with the pen. Therefore, brush work does not resist etching so well and must not be treated too powerfully. Much depends on the treatment of the brush and the consistency of the ink. The brush does not permit such a flow of ink as does the pen, and generally requires one that is more fluid. A good brush ink is made as follows:—