By Abdul Wahid Saleem
Offset printing is a commonly used printing technique in which the inked image is transferred 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 image carrier on which the image to be printed obtains ink from ink rollers, while the non-printing area attracts a water-based film, keeping the non-printing areas ink-free.
St. Joseph Press is an offset printing press located at Mannanam, Kottayam. The press has had its presence for over a century. They printed newspapers like ‘Deepika’ before they set up their own printing press. St. Joseph Press covers everything from printing to binding a finished book.
When we reached the press they were printing a book cover for an engineering college. The people there were patient enough to spare some time from their work and explain each and every part of the offset printing process. They have two offset printing machines, one is for printing smaller paper like bill book, receipt etc. and the other for larger printing like books, covers etc.
The latter one was the most used printing machine at the press. The machine was manufactured by HMT and has the feel of a tiring long run it had been through. It is a ‘semi-automatic’ printer in which one has to adjust the colours manually and do a trial run to check the color. It can print 4000 pages per hour in a single colour.
The process begins with stacking up papers on one end of the machine known as the Seat board. The stacked papers are taken one by one into the machine with the help of a gripper and a blower. The gripper ensures that only one paper goes into the machine at a time by sucking the paper on the top by means of vacuum and placing it on to the machine. The blower makes sure that the papers don’t stick together by blowing a steady stream of air between the papers to facilitate the gripper to take them in.
The papers are of various sizes depending on the thing to be printed. Demy size of paper was used for printing the covers of the book. Other sizes include half-demy, double-demy, foolscap, crown etc.
The paper then goes through the impression cylinder that is connected with the blanket cylinder that in turn is connected to the plate cylinder. The plate cylinder is the place where the stencil is placed. The stencils are designed in a computer and are printed on aluminium sheets. A steady supply of ink is delivered to the plate cylinder from the cartridge connected at the top of it. Beside the plate cylinder is another small cylinder that adds water to the plate cylinder.
The oil based ink used in the offset printing is immiscible with the water applied on the stencil and hence will be applied only on the area where the paper is not wet. The blanket cylinder is where the impression of the stencil is created by paint. From the blanket cylinder the impression is transferred to the paper while it moves through the impression cylinder. The process has to be repeated four times for each colour cyan, magenta, yellow and key colour (black).
The mini offset printer also works in a similar way like the offset printer. The only difference is that it is completely automatic and cannot print large papers. The stencils used in mini offset printing are made from a different kind of paper.
Depending on the purpose of printing the quality of paper used is also changed accordingly. The GSM (Grams per Square Meter) of the paper defines its quality, the more the GSM the more the quality of the paper.
On one corner of the press was the grandfather of printing machines, a letterpress printer which was under the wraps and non functional. Near the letterpress printer in a small wooden shelf were long metal pieces which on a closer look were the alphabets used in the letterpress printer.
The letterpress printer and the offset printer beside each other tells us a brief on the evolution of the printing press.