As illustrated in my previous post, this cover was to commemorate the 1st Malaysian Stamp Exhibition. It was printed by Philatelic Society of Malaysia ("PSM"). I guess the printer engaged by PSM has not check the product properly and thus this cover was obtained by the public.
The printing process for this cover is very much similar to the printing of the stamp, where a technique call "offset lithography" is used.
For stamp printing, full sheets of paper are transferred through the printing press by means of grippers, which ensure that the positioning of the colours is exactly right. The colours are printed consecutively, usually the darkest first and the lightest last, although this order may change if the design demands it. The color normally use includes the three primary color (red, blue and yellow) and black. Sometime while or special color (such as gold or silver) may be used. The overlaping of the primary color could create all type of other colors, for instance blue and red become purple, red and yellow become orange etc. As you can see on the picture above, the overlaping of "red" in the cover above has not been accurate, thus created this "error".
Because the modern offset press works at very high speed, the inks have to dray almost instantly if smudges are to be avoided. Several different drying methods are used. The conventional one is to spray a fine powder on to the printed sheet, which not only speeds the drying process but forms a barrier between the sheets when they are stacked. In addition, catalysts may be added to the inks. In UV printing, an interesting new technique, the inks contain additives which react to UV lights in the press, drying them almost instantly.
Obviously the density of the inks and the strength of the colours have to be very carefully controlled. Also, if the colours are going to print exactly in line with one another, the paper has to be positioned under the cylinders within pinpoint accuracy. Final adjustments are made at a computer console which controls every operation of the offset machine. The skilled operator will regularly pull a sheet from the press and examine it closely, noting any defects, any changes in colour balance or density or any necessary adjustments to the registration.
"Pic showing the printing/engraving process of stamps"
Lithography works on the principle that water and oil repel one another. The offset machine has three main cylinders. The first carries the zinc plate with the image to be printed. The second is a rubber blanket which transfers the image and the third (the impression cylinder) carries the paper. Oil-based ink is transferred from ink ducts via a series of inking rollers to the printing plate. It adheres only to the areas which are to be printed because the rest of the plate is kept damp. As the rollers rotate, the ink is transferred to the rubber blanket which, in turn, transfers it to the paper travelling over the impression cylinder.
The printing process, although noisy, is remarkably quick, clean and efficient. Only two people are needed to control the giant offset machine, along with another to load the paper and ensure the free flow of the inks. Now anyone familiar with basic printing techniques will recognise all the above. It is fairly run-of-the-mill printing technology, albeit at the highest levels of skill and on an impressively large scale.