Bring to class three examples of different types of printing.

Offset Lithography
Offset printing is a widely used printing technique where the inked image is transferred (or "offset") from a plate to a rubber blanket, then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a film of water, keeping the non-printing areas ink-free.

Gravure
Rotogravure (gravure for short) is a type of intaglio printing process, in that it involves engraving the image onto an image carrier. In gravure printing, the image is engraved onto a copper cylinder because, like offset and flexography, it uses a rotary printing press. The vast majority of gravure presses print on reels of paper, rather than sheets of paper. (Sheetfed gravure is a small, specialty market.) Rotary gravure presses are the fastest and widest presses in operation, printing everything from narrow labels to 12-feet-wide rolls of vinyl flooring. Additional operations may be in-line with a gravure press, such as saddle stitching facilities for magazine/brochure work.

Letterpress
Letterpress printing is a term for printing text with movable type, in which the raised surface of the type is inked and then pressed against a smooth substance to obtain an image in reverse. In addition to the direct impression of inked movable type onto paper or another receptive surface, the term letterpress can also refer to the direct impression of inked media such as zinc "cuts" (plates) or linoleum blocks onto a receptive surface.

Flexography
A flexo print is achieved by creating a mirrored master of the required image as a 3D relief in a rubber or polymer material. A measured amount of ink is deposited upon the surface of the printing plate (or printing cylinder) using an anilox roll. The print surface then rotates, contacting the print material which transfers the ink. Originally used as a method of printing onto corrugated cardboard, which has a very uneven surface. It is required that the printing plate surface maintain contact with the cardboard, which it does by being flexible. Also, unprinted high points on the cardboard must not get printed by ink remnants not on the plate surface, which is achieved by ensuring a sufficient depth for the non-print areas of the plate.

Screenprinting
Screenprinting, silkscreening, or serigraphy is a printmaking technique that creates a sharp-edged image using a stencil. A screenprint or serigraph is an image created using this technique.
It began as an industrial technology, and was adopted by American graphic artists in the early 1900s. It is currently popular both in fine arts and in commercial printing, where it is commonly used to print images on T-shirts, hats, CDs, DVDs, ceramics, glass, polyethylene, polypropylene, paper, metals, and wood. Graphic screenprinting is widely used today to create many mass or large batch produced graphics, such as posters or display stands. Full color prints can be created by printing in CMYK (cyan, magenta, yellow and black). Screenprinting is often preferred over other processes such as dye sublimation or inkjet printing because of its low cost and ability to print on many media.

Collotype
Collotype is a dichromate-based photographic process developed for large volume mechanical printing before the existence of cheaper offset lithography. It can produce results difficult to distinguish from metal-based photographic prints because of its microscopically fine reticulations which comprise the image. Many old postcards are collotypes. While no longer a commercial process, its possibilities for fine art photography were first exploited by Todd Walker in the 1970s.

Xerography
Xerography (or electrophotography) is a photocopying technique developed by Chester Carlson in 1938 and patented on October 6, 1942. He received U.S. Patent 2,297,691 for his invention. The name xerography came from the Greek radicals xeros (dry) and graphos (writing), because there are no liquid chemicals involved in the process, unlike earlier reproduction techniques like cyanotype. Xerography is used in most photocopying machines and in laser and LED printers.

Digital print
Digital printing is the reproduction of digital images on physical surface, such as common or photographic paper, film, cloth, plastic, etc. It can be differentiated from litho printing in many ways, some of which are; Every impression made onto the paper can be different, as opposed to making several hundred or thousand impressions of the same thing from one set of plates, as in traditional methods. The Ink or Toner does not absorb into the paper, as does conventional Ink, but forms a layer on the surface. It generally requires less waste in terms of chemicals used and paper wasted in set up.

Definitions courtesy of www.wikipedia.com