There are four general categories of traditional printmaking: relief printing, intaglio, planographic, and stencil processes. Leaving aside the more recent addition of digital means for the moment, we can speak of a print belonging to one of these four categories from a couple of different angles. Identification of print type is made using several indicators , most commonly through the association between the materials used to make the matrix (plate, screen, block, stone, acetate) and the manner in which it is printed.
With stencil printing, images are made by forcing ink through a shaped opening. The term pochoir, French for stencil printing, refers to the most direct process whereby the stencil is hand cut from paper or thin plastic. Ink is applied to the paper through the stencil openings with a stiff brush. Contemporary versions can often be seen in spray painted graffiti. Screen printing makes the stencil slightly more stable by creating one that is attached to a fine screen, traditionally made with silk. The screen mounted stencil allows for every intricate bit of information to be printed.
In fine art printmaking, the relief print is associated with the woodcut, wood engraving and linocut. The materials are carved and the printed image is made of what is left of the original surface. The result tends to be high contrast, although some wood engravings can have quite subtle tonal ranges produced through textural cutting, such as cross-hatching. The ink surface of the print is generally smooth, with an embossment of the block. This embossment is traditionally minimal, but can be exaggerated for enhanced relief effect of the printed surface.
Intaglio prints are traditionally associated with the metal plate matrices which are engraved or chemically etched to establish the image. Traditional platemaking processes can be further divided into two basic categories. Direct processes include engraving and drypoint. Etching involves the use of acid to create the image. Within the subcategory of etching are designations that refer to how the plate was made. These include line etching, essentially a linear approach, and soft-ground, which allows for textural effects. Aquatint is a term often used independently to refer to a specialised etching process that results in a tonal image.
An intaglio print records the opposite of the relief. instead of inking the top surface, ink is added to the depressions and recesses of the matrix. An impression is made by pushing dampened paper into these areas to pull the ink out. In the finished print, the ink layer sits up on the surface. This almost sculptural quality of mark is often one of the most coveted attributes of the intaglio print. Another tell-tale sign of the intaglio print is the evidence of the plate embossed into the paper. This is called the platemark. It is not visible in bleed prints, which are prints made with paper which is smaller than the printing element causing the image to bleed over the edge of the paper.
The word collagraph comes from the union of two words, collage and graphic, implying a connection between the method of construction and the subsequent printing of an image. A traditional collagraph matrix is made in the manner of collage; cutting and pasting paper and other textural elements. Rather than existing as an end its self, the plate is then printed in intaglio and/or relief methods. The visual characteristics of the inked surface are similar to intaglio and relief qualities, but the fact that the plate is constructed in the collage manner is usually discernible.
As print artists have explored a variety of material possibilities, the category of collagraph had expanded to include printing matrices that are made with a combination of techniques. Photo-collagraphs employ light-sensitive films or emulsions to establish information.
Other recently developed material technologies, such as photo-sensitive plastics are often used in either intaglio or relief manners. In such cases, the resulting print is identified by the manner of printing.
Embossings are essentially inkless images produced by impressing dampened paper into the surface of any relief or intaglio plate. The result is essentially a low-relief sculpture.
Lithography is the planographic process. What prints in a lithograph is what is drawn on the surface of a stone or plate. Lithography is a chemical process based on the principle that oil and water down mix. The artist draws on a specially prepared flat stone or metal plate with a greasy substance. The stone or plate is then chemically processed to create mutually exclusive printing and non printing areas.
The surface of a lithograph is smooth. Ideally, the ink is absorbed into the paper. It can be difficult to discern the order of printed colour.
Many contemporary printmakers employ a mixture of different processes. Their interest is less in the purity of a particular medium than in the appropriateness or efficiency of an approach to realise an idea. Sometimes, processes are used as modifying agents in other processes. This is especially true of stencils, which are regularly employed in relief, intaglio and lithography practices.
Combining processes has some technical implications, but in the end, the point is to make good art.