Offset Litho Duplicating
Equipment Required
Duplicator
Plate-making equipment (not always, essential), e.g. printing box and processing unit
Plates
Paper
Ink
Plate making materials
Method
This process is far more complex than the previous two methods of duplicating. In fact, it is more like printing than a duplicating process, and gives a much better overall quality to the finished copy, including illustrations.
Master Preparation
By hand, typing, electrostatic copying, or photographic copying. Line drawings and contrasting photographs possible.
Duplication
In lithographic process the plates can be either paper, plastic, or metal. Paper plates for short runs are cheaper and easier to prepare than metal plates (for longer runs). Cost increases with quality. Paper plates are usually used once, whereas metal plates have an almost indefinite life. Paper plates can be prepared directly by the use of special grease-based pencils, ink or ribbons.
Alternatively, the image of an original can be produced by means of an electrostatic copier, or by photo-transfer. The plate is attached to the drum of the duplicator and a supply of grease-based ink and a watery fluid are applied to it simultaneously. The inked image is not transferred directly to the copy paper, but is brought into contact with another drum which transfers the mirror image created on this drum to the copy paper.
Use
Offices, educational institutions and &hose-built reprographic facilities e.g. bulletins, promotional literature etc.
This is a more expensive option in terms of equipment and maintenance but may be economic where longer runs (see 'economic runs') are required.
Copy Quality
Good - excellent
Colour
Multiple colours possible so long as machine role sink fountain, etc: changed. Accurate registration possible
Economic Run
Advantages
The process is well-suited to the production of office forms, particularly those with complex rulings. A very large number of copies can be obtained. It is a cheap form of printing. Compared with normal printing, cost of printing is lower by 30% to 40% in offset litho printing. The quality of production is much better as compared to stencil duplicators. Master can be stored for an indefinite period. Copies can be obtained with the help of master whenever required.
Disadvantages
Separate runs are required for printing in different colours.
- It can be run only by trained operators.
- It is costlier than other duplicating machines.
- It requires sufficient office space for storing chemicals, plates, and paper etc.