PREPAIRING THE STONE
The stone to be ground is placed on the graining table and thoroughly washed with water. All surface dirt and grit must be carefully removed. Grinding may then begin, using either a levigator or a second stone. Grinding of larger stones is both easier and quicker with the levigator. The use of two stones permits both to be grained at once. This method, although safe and effcient when the two stones are of similar size, must be used with great care when one stone is much smaller than the other, for uneven grinding can easily come about.
When two stones are ground together, the drawing on the upper stone will be effaced more quickly than the drawing on the lower stone; hence grinding should begin with the darker and heavier image on top. Midway in the graining process, the position of the two stones should be reversed.
The stone should be covered with a thin film of water when the abrasive is sprinkled on. Only experience will indicate the corrcet proportion of water to abrasive. If too much abrasive is used and not. enough water, the grinding will be difficult and exhausting, although grinding action will be faster. If too much water is used, the abrasive will flow off the stone, and the grinding action will be lessened. Curiously, it will be found that either too much or too little abrasive will tend to cause scratches. Such scratches should be avoided, for extra grinding is needed to remove them. If not removed, the scratches will appear as lines in the finished print.
Whether a stone or a levigator is used, a regular pattern of grinding should be followed. For small stones a figureeight pattern works well. An equally good pattern, also suited to larger stones, may be ground in a regular series of rows or bands, first horizontally across the stone, then vertically, alternating at regular intervals.
Whatever pattern is used, the basic consideration is to ensure that all parts of the stone’s surface receive the same amount of grinding. To grind longer in one spot than another will cause uneven abrasion and destroy the level of the stone. Grinding should begin with the coarser grades of carborundum, followed successively by finer grades, until the desired surface is attained. A standard procedure is to start grinding with #100 grain, continuing until the previous drawing on the stone has disappcared and has been replaced by its negative image The areas that were dark in the drawing will now appear bright, as in a photographic negative.
From two to six separate grindings are normally required, each with fresh abrasive. Grinding should continue until a rather stiff and dry sludge gathers, at which time it is necessary to wash the stone and levigator thoroughly with water, removing all abrasive and stone particles, which can cause scratches in subsequent grinds. Special attention is required when switching from one grit to another. Should one coarser grain of carborundum remain, it will surely cause scratching. Accordingly, great care should be exercised in storing grit in properly marked containers. Never fill empty containers with the wrong particle size.
Sometimes during grinding it will happen that two stones stick together Suction takes place because of the evenneaa of tle two aurfaces and the adhesive character of a dry graining sluclge. Never under any circumstances try to knock such atones apart, for they will surely crack or break. Try instead to squirt water between their edges or to insert the tip of a thin knife. If a small amount of air can get between the stones, they will separate easily. After the old image has disappeared, the grinding normally continues with two grinds of #180, followed by two grinds of #220. This will be sufficient for most work. The #220 gain is suitable for most techniques and procedures in lithography as the gain most commonly used.
When the grinding has been completed, the edges of the stone are carefully beveled and rounded, especially at the surface edge of the stone, so that ink from the roller will not be caught by the edge in printing. A coarse file or stone rasp is used for this work, followed by a block of pumice or a fragment of lithograph stone. The stone is then washed thoroughly and dried. A sponge or the palm of the hand may be used to remove water and hasten drying. The stone is then taken from the graining table and placed on edge on the work table, preferably on a clean sheet of newsprint. Wet stones are like blotters and will absorb dirt or dust from the surface on which they are resting as if by capillary action.
Stones that have depression or are thicker at one end than the other will print poorly. Testing is done with a metal straightedge and a strip of newsprint paper. When the straightedge is placed across the stone over the strip of newsprint, it should not be possible to move the paper without tearing it. The test is repeated at many places and in all directions. If at any point the strip can be moved, a depression in the surface of the stone is indicated. Irregularities thus located may be spot-ground with the levigator or a small lithographic stone. This takes time and care; but, once a stone is level, it is easy to keep it that way through proper grinding.
When the stone is dry it is ready to receive the artist’s work. If not to be used at once, the grained surface should be covered with clean paper, taped to the edges of the stone. When storing stones, it is advisable to make note of the grain on the covering paper.