SheetFed Offset Lithography Essay Research Paper SheetFed

Sheet-Fed Offset Lithography Essay, Research Paper

Sheet-Fed Offset Lithography

Without printing, where would the world be. Edward George Bulwer-Lytton wrote, The pen is mightier than the sword. But he assumed that his penmanship could be widely distributed and studied (Adams 7). Printing creates a means for information to be recorded and passed down from generation to generation. Prior to the invention of printing, all information had to be conveyed verbally and survived only as long as people could remember. Printing created the power to document information and pass it onto younger generations. Printing is the ability to reproduce graphic symbols and messages in large quantities. With thanks to the invention of printing, we are able to have our ideas mass-produced and keep the world informed (Adams 3). Since printing is such an essential segment of the society that we live in, it is vital that the public has a general understanding of the history, concepts, and processes that involve printing.

The invention of printing and a practical moveable type is credited to Johann Gutenberg around 1454. This invention earned Gutenberg the title of father of printing (Adams 2). The process of printing that Gutenberg invented is relief printing, or printing from a raised surface. Even though this process of printing is no longer commonly used, it is still the foundation of present day offset lithography.

Lithography was invented by a German playwright who was invented with the printing process to try and lower the cost of printing his plays. This man was Alois Senefelder and the year was 1789. Senedelder experimented with many different ways of printing, but found the best and cheapest way was to etch the image he did not wish to print on a stone, leaving a raised image of the desired area. This raised area could then have ink applied and paper pressed to it and the image would be created. This is an adaptation of the relief printing process. Senedelder named his invention of printing from an etched stone lithography, based on Greek words lithos, meaning stone, and graphein, meaning to write. The lithography process of printing developed a reputation for quality and fine arts through the Currier and Ives Company that operated in America from 1835 to 1895 (Adams 289).

Printing must first start with a sample of what is to be reproduced. With today s technology, this sample, or copy, is almost exclusively created with a computer. While it can be made by hand, a computer is the easiest way to fashion a copy. Specialized software can help in creating a product to be printed. Desktop publishing software brings together many elements that are helpful at doing this. This software works well with type fonts and images and can help integrate them into a pleasant looking sample to be printed. If just text is desired, word processing software can be used to input and edit the transcript. Word processing software can easily check for spelling and grammar errors and can effortlessly change the appearance of the type. Once the desired copy is created, it must then be printed on a computer printer in black and white to be moved onto the next process (Dennis 57).

Once a preferred copy of what is to be printed is made, that copy must be photographed and made into a negative. This is done in the same way that a regular photograph is obtained, but only on a larger scale. The copy is place in front of a large camera and held on a copy board. The camera is then loaded with film and exposed to the copy. The film is then developed in a darkroom by a chemical process similar to that of developing camera prints. This developing must be done in a darkroom with special red lights to protect the light sensitive film from being exposed and ruined. The size of the developed negative is usually the same size as that of the copy that was photographed. The finished negative is named such because it is the exact opposite as the copy that was photographed. Where the text was on the copy, the negative is transparent, and where the copy paper was white, the negative is black and opaque. Once the negative is developed, it is ready to be made into a flat (Adams 219).

Stripping is the process of applying the negative onto a piece of paper called a masking sheet, or flat. To do this, a table with a glass top and a source of light below it is used. The masking sheet is squared up on the light table and the negative is positioned under the flat where it is to be printed. The negative can be easily seen as a result of the light from the light table shining through the top. Once the negative is in the desired position, holes are cut in the masking sheet where the image area is located. To keep the negative from moving, tape is applied to the cut edges of the flat and onto the negative. If the negative is not stripped straight onto the masking sheet, an uneven product will be printed. To cover up areas that are not desired for the printing, a red tape is applied to these areas. This red tape will prevent the covered image from being reproduced. Once the negative is correctly stripped onto the masking sheet, it is ready to make a plate (Dennis 278).

Lithography printing plates are made from a thin sheet of aluminum and coated with a light sensitive material that hardens when it comes in contact with bright light. The masking sheet and negative are aligned on top of the pla