Lithography (from Greek λίθος - lithos, 'stone' + γράφειν - graphein, 'to write') is a chemical method to create an image using a stone (lithographic limestone) or a metal plate with a completely smooth surface. This is chemical process based on the principle that oil and water do not mix, and resist one another.
     The artist draws the image directly on a highly polished limestone using a grease-based pencil, wax crayon or grease-based liquid called tusche, like it does on paper or canvas. A wide range of oil-based media is available, but the durability of the image on the stone depends on the lipid content of the material being used, and its ability to withstand water and acid. In fact, the way it is prepared makes the stone surface or plate to look like paper - the stone is handled by a velvet structure through the use of abrasive powders. In the case of lithography on stone that is really a substitute for heavy paper - the weight of the stone sometimes exceed 300 kg. It takes several people to move the paintings of the artist.
     To stabilize the drawing and the parts that are not printed ink not take the stone's surface is covered with talcum powder. After the drawing of the image the stone is prepared for printing by applying a chemical solution of gum arabic, weakly acidified with nitric acid HNO3 to make it more receptive to water. The gum solution penetrates into the pores of the stone, completely surrounding the original image with a hydrophilic layer. It.s divided into hydrophilic regions that accept a film of water, and thereby repel the greasy ink, and hydrophobic regions that repel water and accept ink. In order to make the print, the stone is dampened with water, which will not adhere to the drawn image because of the natural antipathy of grease to water. Ink is rolled on a wet stone. Oil-based retain water and accept ink which can not cover the wet parts of the stone. For instance, the positive part of an image is a water-repelling ("hydrophobic") substance, while the negative image would be water-retaining ("hydrophilic"). When ink is rolled over the stone, it will only adhere to the grease-based image. Then the paper is pressed against the stone, and only the ink on the greasy image is transferred. The press is specifically designed not only to bear the burden of stones, but also enhances the exceptional pressures that are used for printing lithographic image. After printing with a special lithographic press the greasy image remains on the stone and the process of moistening, inking and printing is repeated. This allows a flat print plate to be used, enabling much longer and more detailed print runs than the older physical methods of printing (e.g., intaglio printing, letterpress printing).
     During printing the stone must be kept wet which is a complex and difficult process. To create a color lithograph, a separate stone for each color is used and must be printed separately.
     Lithography, invented in 1786 by the German Alois Senefelder, is based on the natural antipathy of oil and water. During the first years of the 19th century, lithography had only a limited effect on printmaking, mainly because technical difficulties remained to be overcome. Germany was the main center of production in this period. Godefroy Engelmann, who moved his press from Mulhouse to Paris in 1816, largely succeeded in resolving the technical problems, and during the 1820s lithography was adopted by artists such as Delacroix and G.ricault. London also became a center, and some of G.ricault's prints were in fact produced there. Goya in Bordeaux produced his last series of prints by lithography.The Bulls of Bordeaux of 1828. Color Lithography or "Chromo Lithography" was developed by Engelmann and Lasteyrie in 1816. In principle handmade Color Lithography requires as many stones as the numbers of colors used. Wunderlich has developed techniques which allow some colors to be printed from the same stone. Rodolphe Bresdin and Jean-Fran.ois Millet also continued to practice the medium in France, and Adolf Menzel in Germany. In 1862 the publisher Cadart tried to initiate a portfolio of lithographs by various artists which was not successful, but included several superb prints by Manet. The revival began during the 1870s, especially in France with artists such as Odilon Redon, Henri Fantin-Latour and Degas producing much of their work in this manner. In the 1890s color lithography became greatly popular with French artists, Toulouse-Lautrec most notably of all. During the 20th century, a group of celebrated artists, including Calder, Chagall, Dufy, L.ger, Matisse, Mir., and Picasso, Alphonse Mucha rediscovered the largely undeveloped art form of lithography thanks to the Mourlot Studios, also known as Atelier Mourlot, a Parisian printshop founded in 1852 by the Mourlot family to promoted the artists' work. M. C. Escher is considered a master of lithography, and many of his prints were created using this process.
     The image can be printed directly from the stone plate, or it can be offset, by transferring the image onto a flexible sheet (rubber) for printing and publication- offset lithography. Offset lithography is one of the major industrial printing techniques and can also be painted by hand like stone, but then be printed on an offset press. In the 19th century there were presses, creating offset prints by hand-painted lithograph stones. There is progress in using this method especially when the image has a written text. The image is subtracted on film or plate and mechanically transferred on a rubber cylinder, which it printed on paper (can also on metal or plastic sheet). This technique is considered only when the original artist handmade paper process - drawing on it with chalk or ink, and it fully formed. Most Offset Lithographs are made up of thousands of tiny dots, easily seen by looking through a magnifying glass, and only 4 colors are used: red, blue, yellow and black. Original Lithographs on stone are made of solid colors.
     High-volume lithography is used presently to produce posters, maps, books, newspapers, and packaging.just about any smooth, mass-produced item with print and graphics on it. Most books, indeed all types of high-volume text, are now printed using offset lithography. Original lithograph should not be confused with offset lithography, reproduced photographically.
     Stone lithography is not so popular these days mainly because of the huge physical effort that requires. Increasingly used the new method called "Mylar transfer". In this modern lithography technique, the image is made of a polymer coating applied to a flexible aluminum plate. The artist draws the image on a sheet of transparent plastic. After transferring the image in a photographic way on aluminum plate printing is done manually or by an offset press. Metal plates for lithography are much lighter and portable, but not create this artistic image as stone. The process is applicable to quickly obtain accurate color on a large circulation and a further advantage is that the painter should not paint backward as in conventional methods. There is no halftones as in mechanically reproducing photographic posters and almost indistinguishable from lithography, printed and painted by hand. Good lithographs printed on stone are almost indiscernible from the original drawing.
     For offset lithography, which depends on photographic processes, flexible aluminum, polyester, mylar or paper printing plates are used instead of stone tablets. Modern printing plates have a brushed or roughened texture and are covered with a photosensitive emulsion. A photographic negative of the desired image is placed in contact with the emulsion and the plate is exposed to ultraviolet light. After development, the emulsion shows a reverse of the negative image, which is thus a duplicate of the original (positive) image. The positive image is the emulsion that remains after imaging. For many years, chemicals have been used to remove the non-image emulsion, but nowadays plates are available that do not require chemical processing.
     A zincography is the same technique, but employing a zinc plate rather than a stone.
     A transfer lithograph (French, autographie) also employs the same technique, but the design is drawn on special transfer paper and is later mechanically transferred to the stone.
     As a special form of lithography, the Serilith process is sometimes used. Serilith are mixed media original prints created in a process in which an artist uses the lithograph and serigraph process. The separations for both processes are hand-drawn by the artist. The serilith technique is used primarily to create fine art limited print editions.
     Many innovations and technical refinements have been made in printing processes and presses over the years but the Bavarian (State of Germany) limestone is still considered the best material for art lithography.
     On the stone can be applied and the technique dark manner by scraping from dark to light (like mezzotint). Then the work is signed as "Negro Litho".