Lithographic printing is a process of printing from a smooth surface of a metal plate or limestone to print on paper or a different substrate to print text or artwork. Earlier this method was used to release theatrical works. This comes under the category of Planographic printing which uses the immiscible property of grease and water such that the image and non-image areas can be easily classified. The image areas are grease-treated and the non-image areas are wet with moisture. Moisture repels ink.
When it comes to Offset, there is no direct printing involved. The ink first gets transferred from the plate to the rubber blanket and from rubber blanket to paper. This method follows the principle of repulsion of oil and water. This method is used for mass-production printing. It is also helpful to lengthen the life of plates. However, the substrate media can be canvas, cloth or wood which have a rough surface.
Irrespective of the volume of the job supplier has Web Offset Printing Machine produces high and uniform quality of images. Offset lithography is basically a three-stage process – pre press, on press and post press.
In Pre-press stage, the files are being transferred from designer to printer. The pre-press department then ensures that all files are properly packaged and all images are high resolution. After this the designer has to choose between spot or processed colors. Then is the stage of proofing that checks for color accuracy and imposition proofs. These proofs must be approved by the designer. This stage is carried out on plate cylinder.
On press stage is a make-ready process in which the ink is pressed on the pressman plates and then a test print follows. The final press-run should be signed by the designer which is followed by the printing of entire job. This stage is performed over offset cylinder.
The last phase is Post-press that will be executed on impression cylinder. The print is then dried on impression cylinder and the piece of work is folded. The final work is then packed into boxes for shipping it to desired destination. It also employs special processes like die-cutting, foil stamping, embossing, thermography etc.
The color scheme used in this process is CMYK that is cyan, magenta, yellow and black. An Offset printer employs labels to the printing work with their reference on the left margin with bold effect on the label fonts.
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