What is an Offset printing ?
Offset printing is a commonly used printing technique in which 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 water-based film (called “fountain solution”), keeping the non-printing areas ink-free.
Development of the offset press came in two versions: In 1875 by Robert Barclay of England for printing on tin, and in 1904 by Ira Washington Rubel of the United States for printing on paper.
The actual process of printing is quite involved. One of the most important functions in the process is pre-press production. This stage makes sure that all files are correctly processed in preparation for printing. This includes converting to the proper CMYK color model, finalizing the files, and creating plates for each color of the job to be run on the press.
Every printing technology has its own identifying marks, as does offset printing. In text reproduction, the type edges are sharp and have clear outlines. The paper surrounding the ink dots is usually unprinted. The halftone dots are always hexagonal though there are different screening methods.
What is a Photogravure (or Heliogravure) ?
Photogravure ( or Héliogravure) is a photographic image produced from an engraving plate-an expensive and rarely used process today. Through the transfer of etching ink from an etched copperplate to special dampened paper run through an etching press, this process creates an image that registers an extraordinary variety of tones. This unique tonal range comes from photogravure’s variable depth of etch–the shadows are etched many times deeper than the highlights unlike the halftone processes that merely vary dot size. The prints produced via this process have the subtle tones of a photograph and the art quality of a lithograph, making them extraordinarily collectible items.
Heliogravure or Photogravure, is the oldest procedure for reproducing photographic images. It was first invented in the early 19th century by Joseph Nicephore Niepce, of France, and later perfected by Talbot, Niepce de Saint-Victor, Baldus and Klic. The process involves two distinct steps. First, in a complex photochemical procedure that creates the intaglio surface, the photographic image is fixed and etched upon a specially prepared copper plate. The finished plate is then placed on a hand-turned press, and the image is printed onto dampened etching paper using special inks.
This traditional method of heliogravure is variously called heliogravure au grain or heliogravure plat. Before receiving the photochemical transfer of the image, the flat copper plate is first carefully dusted with rosin powder; it is then heated, so that the microscopic grains of rosin melt into fine droplets and fuse to the metal. It is this that accounts for heliogravure’s exceptional tonal range, for when the plate is subsequently etched, the acid only reaches the copper through the fine interstices existing between these grains.
The transitions from light to dark are thus modulated with extreme precision and subtle nuance. Even when examined under a magnifying glass, a heliogravure betrays no screen pattern, unlike images printed using industrial methods such as offset, letterpress or rotogravure.
Heliogravure belongs to the same family of intaglio printing techniques as engraving, etching and aquatint. As such, it requires an especially good quality of thick paper, one that can draw out the ink from the furthest recesses of the etched copper. In like manner, the plate embosses the finished prints, for its form is impressed into the dampened paper as they pass together through the rollers. Printed by hand in limited quantities, each heliogravure is considered an original, and its value is accordingly assured.
What is a Lithograph ?
Lithography originally used an image drawn (etched) into a coating of wax or an oily substance applied to a plate of lithographic stone as the medium to transfer ink to a blank paper sheet, and so produce a printed page. In modern lithography, the image is made of a polymer coating applied to a flexible aluminum plate. To print an image lithographically, the flat surface of the stone plate is roughened slightlyetchedand 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 because the surface tension is greater on the greasy image area,which remains dry. The image can be printed directly from the stone plate (the orientation of the image is reversed), or it can be offset, by transferring the image onto a flexible sheet for printing and publication.
As a printing technology, lithography is different from intaglio printing (gravure), wherein a plate is either engraved, etched, or stippled to score cavities to contain the printing ink; and woodblock printing, and letterpress printing, wherein ink is applied to the raised surfaces of letters or images. Most types of books of high-volume text are printed with offset lithography, the most common form of printing technology. Etymologically, the word lithography also denotes photolithography, a microfabrication technique used to make integrated circuits and microelectromechanical systems, as such are more technologically akin to etching than lithography, printing from a stone plate.
What is a Serigraph ?
Serigraph or screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil to receive a desired image. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate. A fill blade or squeegee is moved across the screen stencil, forcing or pumping ink into the mesh openings for transfer by capillary action during the squeegee stroke. Basically, it is the process of using a stencil to apply ink onto another material whether it be t-shirts, posters, stickers, vinyl, wood, or any material that can keep the image onto its surface.
Screen printing is also a stencil method of print making in which a design is imposed on a screen of polyester or other fine mesh, with blank areas coated with an impermeable substance. Ink is forced into the mesh openings by the fill blade or squeegee and onto the printing surface during the squeegee stroke. It is also known as silkscreen, serigraphy, and serigraph printing. A number of screens can be used to produce a multicolored image or design.
What is a Photograph ?
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film. Typically, a lens is used to focus the light reflected or emitted from objects into a real image on the light-sensitive surface inside a camera during a timed exposure. The result in an electronic image sensor is an electrical charge at each pixel, which is electronically processed and stored in a digital image file for subsequent display or processing. The result in a photographic emulsion is an invisible latent image, which is later chemically developed into a visible image, either negative or positive depending on the purpose of the photographic material and the method of processing. A negative image on film is traditionally used to photographically create a positive image on a paper base, known as a print, either by using an enlarger or by contact printing.