Stencilling is one of the simplest ways to use a number of colours combined with an intaglio plate. This method has advantages and also limitations. The main advantage is that it eliminates the registering problems of intaglio colour printing. On the other hand, it is limited to flat, sharply defined colour areas. One method does not replace the other, but each may be used to solve a particular problem.
The procedure itself is very simple. The intaglio plate is inked and wiped normally. The desired colour shape is cut out on a stencil paper. The stencil is placed on the already inked plate and the colour is rolled onto the surface of the plate using a gelatin or soft rubber roller. For surface rolling, regular artist oil colours can be used. The use of stencils allows a great number of colours to be printed with a single run on the press. This is done by surface rolling colours through stencils onto the intaglio inked and wiped plate surface.
For more complex colour combinations, it is possible to combine colours stencilled directly on the paper with colours offset from the intaglio plate. For more sophisticated stencilling, silk screen can be used also in combination with the intaglio plate. When intaglio and stencilling are combined, the process is often designated as mixed or combined technique. This is essentially the same procedure as conventional stencilling except that with silk screen more complex designs and textures can also be stencilled on the plate (see below Stencil processes). Intaglio and surface colour with relief etching
In this technique the main colour structure is defined by the plate surface, which is etched to different levels. The linear or textural elements moving from one level to another bind the whole together.
The sequence of printing begins with the intaglio inking and wiping of the plate. Next, the first surface colour is rolled on with a soft gelatin roller that penetrates the lower levels of the relief. The high areas are inked with a hard rubber or composition roller. The sequence of rolling can change, according to the demands of the particular colour problem.
In addition to plate levels and roller variety, control of colour viscosity is an important factor. The thorough description of this method is so complex that the reader is referred to some of the technical books listed in the Bibliography. Surface-printing processes
Surface printing comprises those techniques in which the image is printed from the flat surface of the metal, stone, or other material. The major surface method is lithography, a planographic process. Although many experts place silk screen and stencilling in a separate category, they can be considered surface-printing processes. In lithography, the control of the design is achieved by the chemical treatments of the drawing surface. In stencilling, the design is created by holes in the stencil and the printing ink is either rolled or squeezed through the stencil onto the paper. Silk screen is a special form of stencilling. Lithography
Lithography is based on the fact that water and grease do not mix. The image is drawn or painted on the stone or metal plate with greasy litho crayon or a greasy black ink (tusche). Once the drawing is finished, it is fixed with an etch to prevent the spreading of the grease. A heavy, syrupy mixture of gum arabic and a small quantity of nitric acid, the etch is used to protect the drawing from water and to further desensitize the undrawn areas to printing ink. The nitric acid opens the pores of the stone, enabling the gum and the grease to enter easily. The gum arabic surrounds the greasy sections, forming an insoluble surface film that sticks to the negative areas and crevices of the grain. This coating around the image repels the water applied during printing and establishes a grease reservoir. It does not smear, and it prevents seepage that would blur the image.
Because of the antipathy of grease and water, the image attracts oily ink but repels water. Thus, when the stone is dampened with a sponge and an ink-charged roller is passed over it, the ink is deposited on the greasy drawing but not on the wet stone.
In lithography, the assumption is that the drawing made on the stone or plate will be closely duplicated on the print. While intaglio processes yield prints unlike any drawing technique, lithography is quite reproductive. Although it is a complex method, if lithography is well done, the effect of the print is deceptively simple and direct, making the technique attractive to artists who wish to avoid the more idiosyncratic printmaking methods.
A highly skilled technician is needed to produce a good lithograph, and most lithography is done in workshops where well-trained workers are available. The artist usually works on the stone or plate under the guidance of master printers. When the artist finishes a drawing, the master printers etch the stone and do the printing. In the basic technique, the first step is the preparation of the stone or plate. If a stone has been used before, its surface must be reground. The stone is placed in a sink and thoroughly wetted, and carborundum powder is sprinkled over it. Then, either with a levigator (a heavy steel disk with a handle) or by rubbing two stones together, the surface is thoroughly reground. From time to time the surface should be tested with a steel straightedge to make sure it is level; otherwise it will print unevenly. After the stone has dried, it is ready for work. It is very important to keep the stone clean because any dirt, particularly grease, will show up on the print. Smudges and dirt can be cleaned off with erasers and abrasives.
Metal plates (zinc or aluminum) can also be used, and these, too, may be reground. Although metal plates are satisfactory, stone is far superior, particularly for producing subtle tones and details.
With litho crayons and tusches the artist can work on the stone as he would on paper. A whole arsenal of effects is available, including pen, pencil, splashing, sprinkling, spraying, texture transfers, and scraping. After the drawing is finished and before etching, the image must be protected from the etching solution by rubbing rosin and then talcum powder on the stone. The acid-resistant rosin protects the drawing; the talcum absorbs the excess grease, allowing the adhesion of the gum etch to the edges of the drawing.
Next, the whole surface of the stone is coated with undiluted gum arabic, applied with a wide, soft brush. The subsequent etching process is done in stages. The weakest acid solution is usually brushed first on the lightest areas of the drawing. After an appropriate interval, the next strength solution is brushed on, and this continues until the strongest etch has coated the darkest areas.
After the allotted time has elapsed, the excess etch solution is blotted with newsprint paper. The surface is then wiped down and buffed with cheesecloth to a smooth, even layer. When properly handled, the stone should appear dry. It should be allowed to stand for two hours before washing out, the next step.
The washout is done by pouring a small amount of turpentine or Lithotine over the drawn areas. Gently rubbing the drawn areas with a clean dry rag removes the drawing through the gum-etch coating. The image is preserved by the absorbed grease in the porous limestone.
Next, the stone is rubbed with liquid asphaltum or printing ink dissolved in turpentine. This procedure saturates the image and protects it at the same time.
After the stone is dry, it is ready to be inked (rolled up). First, it is dampened with a wet sponge. (In between the rollings, the stone should be redampened.) Ink rolling should be carried out according to a set pattern, gradually building up the image. To facilitate the even distribution of ink it is important to use a roller wider than the image.
The lithographic press prints with scraping pressure. The press itself consists of a metal frame that accommodates a travelling steel plate (the bed), which passes with the stone under a scraping bar (or yoke). The bed can be lowered (to position the stone) and raised (to print). The pressure on the scraping bar can be adjusted.