Basic lithographic process

Processing the drawing to prepare it for printing is one of the critical phases of lithography. Because mitsakes at this point can easily destroy the drawing on the stone, the greatest care must be taken to proceed correctly and to understand fully each step involved.

The aim of processing is to scparate chemically the image and nonimage areas of the drawing so that they will receive or reject ink consistently. When proicessing begins, the image areas consist of pasages drawn with greasy lithographic crayon or tusche. Through chemical processing the fatty-acid particles contained in the drawing are liberated, permitting them to combine with the stone itself. Once the grease has been transferred, there is no further need for the drawing materials that contained it. The greasy areas are now ink-attractive and form the printing image. Simultaneously, the undrawn or nonimage areas are so treated that they will receive water and repel grease. This reaction is brought about through a process called etching, in which a mixture of gum arabic and acid is applied to the stone, desensitizing its surface. The strength and formulation of the etch is determined through consideration of the character of both the lithographic drawing and the stone.

A sequence involving two separate etches is employed. The first etch partially desensitires the stone, so that the drawing materials may be removed with solvent, a proress called the washout. The cleaned image, now an integral part of the stone, is inked with a roller, a process called the roll-up. The inked image is then given a second etch to complete the desensitization of the stone and to provide a durable separation of ink-attracting and ink-rejecting areas during subsequent inking and printing.

1

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.

2

DRAWING

Before starting to darw on the stone, the edges of it should be protected with arabic gum. It helps to keep them clean. After deciding about the dimensions of the future drawing, you should draw the rectange on the stone and cover the edges with thin layer of gum arabic with soft brush. When the gum will be dry, areas of the stone covered with it will be protected against the grease. Limestone is very sensitive material, so even clean hand can live a trace that will apear during the printing process. All dirts and oliy traces can be removed with sandpaper, sandstone or sharp tools. Protecting the edges with layer of gum helps to keep them clean and saves the time.

When the layer of gum is completely dry – drawing can be started.

Lithographic crayon is one of the most popular materials in classical lithography – its easy to draw and easy to prepare the drawings made with it. Usually processing and printing the images made with crayon goes well. Just after finishing the drawing, image can be etched – there’s no need to wait until it will be dry. Drawing with lithographic crayoon is similar to drawing with pencil or regular crayons on paper. You have to remember that as in allmost all printmaking techniques – the image should be mirrored. It is very important especcially when you draw text or portraits.
The crayons leave oily traces on the stone – lithographic crayons are made of greasy material. In magnification – the particles of grease stick to the rough surface of the stone. When drawing blacks, it’s better to add multiple layers of sharp crayon drawing than to press hard. The graesy crayon can make the “bridges” with undrawn areas underneath.

3

ROSIN AND TALC

Drawings to be processed must first be protected with a resistant material in order to withstand the corrosive properties of the acid contained in the etching solution. Rosin and talc (French chalk) are used in the process, each performing certain tasks better than other. Rosin is the major etch resist because it possesses the following properties:  it is avalaible in a finely ground fluorlike form;  it is insoluble in water; it is soft and easily soluble in turpentine; it is easily melted by heat; and its particles bind together instead of remaining separated under the acid. Talc also is unaffected by nitric acid; however, it does not exhibit the uniting properties of rosin, and it tends to separate under waterly solutions. Consequently, talc is not recommended as an absolute resist. Its most valuable function is to overcome the tendency of the greasy image to repel the watery solutions of gum and etch. By destroying surface resistance, it permits these solutions to lie more evenly on the work during the course of etching.

Since the rosin is accepted as the major acid resist, it should be applied to the image before talc.

Both rosin and talc must be used also in the second etching. They should be applied separately. Mixing talc and rosin together for application in a single operation is not recomended – the rosin particles will be attached first to the ink; hence the protection of the image agains the etch could be uneven. Both rosin and talc are gently applied to drawn and inked surfaces witch tufts of cotton or soft brushes; all excess powder is removed after each application.

 

4

ETCHING THE STONE

The etching solution is tested on the borders of the stone, to determine the strenght of reaction on that particular stone. The contact of the acid mixture with the carbonates of the stone will produce an effervescence of carbonic gas bubbles, which will indicate the strenght of the etch. If the reaction is violent and instaneously produces a rich white froth, the etch is probably too strong; it should be diluted with gum arabic. A satisfactory etch should react almost instantanelously, producing a gentle frothing. Weak etches will not efferversce until several second have elapsed; then they do so very mildly. Strong etches applied through pools of gum react like weak etches. If the etch appears too strong during application, it should immediately be diluted by adding gum arabic, or it should be brushed away from the drawing and toward the borders of the stone. Such etches should not be removed with a dampened sponge, because the water-soluble ingredients of the drawing may be endangered or smeared.

The basic application procedure is to flow the etch across the whole stone, rapidly and evenly subjecting all areas of the image to equal amounts of solution. The area of the stone to be etched may be reduced by first covering all the borders with the etch. Next a generous brushful of etch is carried in a single sweep across the top of the image from one side to the other. The brush is charged again and a second stripe is carried across the stone, just overlapping the first. The brush will need reaching for each stripe, because its solution will be partically exhausted as well as somewhat neutralized by reaction with the limestone. This pattern is repeated until the entire stone is covered. At the same time the strongest effervescence is brushed away from the weaker areas of the drawing and is deposited on the stronger. When the stone is completely covered, the remainder of the solution is applied more deliberately, at right angles to the first application. Further manipulation of fluid over the greasier areas of the drawing is advisable at this time.

The etching should proceed with continous manipulation for two or three minutes; after this the total volume of the solution an dmost of the chemical reaction will have been spent. The etch should not be left on the stone too long, however, for it cannot then be dried into a thin coating.

The tinner and evener the coating, the better will be the desensitization of the stone. The wiping and polishing technique forces the film of etch or gum into the valleys of the stone grain and exposes the image for easy solvent removal during the washout. The adsorbed films of the etch or gum coating serve as a water-bearing and ink-rejecting mask, covering each grain and pore of the nonprinting surface. Coatings that are too thick or uneven often cover parts of the drawing, making it difficult for the washout solvent to penetrate and dissolve the image. Moreover, unevenly adsorbed coatings cannot retain water films equaly, hence they impair the inking of the image and can, in serious cases, produce gum streaks which are impossible to remove from the stone and which appear on the impressions printed from it.

Etch an gum coatings should be dried with two folded cheesecloth pads; the first mpos up and evens the bulk of the etch solution, and the second polishes and dries the remainder to a thin, even film.

When the first etch is thoroughtly dry, either the stone can be washed out, rolled up, and given a second etch or it can be stored for future completion the processing. It is preferable to complete the processing by inking the stone and giving it a second etch before storing for long periods.

 

5

THE WASHOUT

After the first etch the fatty components of the drawing become an integral part of the stone, and the nonprinting image comprises a surface that is partially water-receptive and ink-rejective. The original ingredients of the drawing materials are no longer needed; these are removed in the washout process, which prepares the exposes image on the stone to receive ink.

The work is washed out through dry coating of etch or gum, using turpentine and clean, dry rag. The solvent has the ability to penetrate the thin etch coating without dissolving it. The etch coating acts as a protective mask over the nonprinting areas, preventing the dissolved sludge from making contact with the stone.

The dissolved sludge is wiped away and the stone is fanned dry, permiting the solvent to evaporate.

After few minutes – asphaltum solution should be applied on the stone with a clean, dry rug.

 

6

ASPHALT

The ink receptivity of a lithographic image is directly proportional to the extent of its fatty deposits. Heavy deposits of grease will tend to attract ink from the roller more rapidly than weak deposits. Hence, during the roll-up, the dark areas of an image will sometimes appear fully inked before the light areas have achieved their full tonality. If the stone has also been inadvertently overetched, even slightly, the light areas will accept ink all the more slowly. Inking further to assist the development of the light areas may result in overinking of the darks.

Liquid asphaltum may be applied to the image to fortify the fatty deposits and to equalize ink receptivity.br /> When liquid asphaltum applised on the image and dried, its greasy constituents fortify the fatty image deposits, leaving a tenacious and tacky film which is highly receptive to ink. Because of its greasy nature, asphaltum is also beneficial in reinforcing areas that have suffered minor grease loss from overly strong etching.

The drawing is washed out througr the dry- gum mask, following the washout procedure.

Asphaltum solution is applied with a clean cloth in an even film over the entire work an then is fanned dry.

The dried coating is washed out with water. This removes the etch or gum mask from the nonimage areas. The image areas will retain a firm tacky coating which forms the ink base.

The stone is kept damp and is immediatly rolled up with ink. It will be seen that the image will accept ink more quickly and evenly. Slightly overetched areas will regain their original value. If they do not, the overetching has been severe, and very little can be done to correct the error without couneretching the stone.

 

7

THE ROLL-UP

The application of ink after the washout is one of the critical phases of stone processing. The objective is to deposit a layer of ink on the image, exactly duplicating the visual characteristics of the original drawing. The inking procedure must be executed with care and deliberation, inasmuch as the stone is only partially desensitized by the first etch.
The roller, lightly charged with ink, is passed over the work rapidly and lightly four or five times without stop- ping. Examination of the work will show that the image is beginning to receive ink in an increasing or decreasing degree, depending on its particular characteristics. The procedure of rapid rolling with minimum pressure limits the discharge of ink and enables the printer to assess the receptivity of the image to the ink. Within the period of the first few passes of the roller, the printer must determine the rolling techniques necessary for that particular stone. If ink acceptance is slow, the rolling should proceed more slowly and with graduall increased pressure. If ink acceptance is fast, rapid rolling and minimum pressure should continue. As the image develops, the roller is recharged with fresh ink from the slab, the stone is redampened, and the rolling is continued. These steps are repeated with periodic inspection of the work until the image is fully charged with ink and duplicates the tonalities of the original drawing.

In this condition it is ready to receive minor corrections; these are followed by the second etch for the completion of desensitization.