The published articles are meant to primarily educate the students in printing to supplement their knowledge in the field of Printing. These are not simple Glossary of printing terms, but to the extent possible every term has been explained in brief so that it can be of some use to the students who appear in some sort of examinations and interviews.
I served the Printing Industry for over 40 years
in various capacities, a major part in an Security Printing Organization. In order not to waste the printing and paper related knowledge which I gained over years, I decided to keep them in public domain for the reason stated in prepara. Most of the illustrations - over 90% - have been generated by me to explain the terms suitably.
While I am not sure to what extent the published content will help, if the content is going to be of use to some one in some manner, I will be greatly satisfied.
Your views may be sent to me (
nrj_1945@yahoo.com) for my record and correction wherever needed.

TOTAL NO OF PRINTING TERMS

POSTED TILL NOVEMBER, 2012

- Over 400 terms-

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Wednesday, June 5, 2013

Intaglio Printing- Doubts on depth of relief



The frequently asked  question is how much relief can be expected out of the Intaglio printing plate  printing on Intaglio rotary machines. Why the Intaglio prints printed on high speed Intaglio machines do not show higher relief compared to the manually made print on a  proofing press which show very high percentage of relief than the machine print ?

First of all it is indisputable fact that the Intaglio print on high speed rotary press can not give very high relief in print as desired by us even though the engraved dies may have deeper pits of image to carry more ink . There are limitations. Read the following to understand the reason.  The images to be printed by Intaglio are all line work and not halftones. The images, be it be a portrait or numeral, or words or some text - they will all consist of fine lines, dots, wavy lines, thick and thin lines etc. The tonal values i.e light and darker shades in the picture will have the above elements in varying degrees of thicknesses and strength (depth).  To fully understand the  limitations in Intaglio printing read the following.

(1) Let us assume that we are going to print an intaglio image as shown below which  has gradations by way of thicker and thinner lines, wavy lines, dashes, small dots etc to give desired  tonal effect in the resultant Intaglio  relief image (High and low depths). 


(2) First the image will be engraved on to a master Die. The final engraved plate for printing will be prepared after  completing certain  processes. The final plate will then be prepared for Intaglio printing. The engraved areas on the plate will have corresponding depths to the printed image required to be printed. The plate will produce relief image using stout ink.


(3) Now the question is when printed on a high speed Intaglio machine whether  the printed  image will have the  same amount of relief  as per engraved plate corresponding to the original ?
  • The real answer is clear 'NO'.
  • The ink from the plate will transfer only to the maximum  extent of  85-90% held in the pits to produce the print.  This means the relief on the print will not be exactly equal to the engraved depth on plate. Supposing the depth of engraving is 0.070 mm the resultant print relief will be anywhere around  0.050mm to 0.055 mm only by high speed machine printing, and around 0.060 in hand made proofs or semi automatic slow speed machine made proofs.
(4) Why ?   Though it is theoretically stated that very high relief is possible, in reality  it is not possible to transfer the entire ink from the pits from  the plates even if you make very deep engraving on the parts requiring more relief  image.  There is limitation to the transfer of the ink on to the paper due to several factors like printing speed, position of the paper pulling out the ink from the pits, the angle in which the ink is pulled out, the stoutness of the  ink etc.  See below two images to understand how the  paper lift the ink from the  plate .

Generally more than 0.070 mm to 0.085 mm depth engraving is not practically made because of the above reasons and very high relief image can not be obtained on high speed Rotary machines.

(5) Actually how does the transfer of ink take  place ? 
 
The Intaglio ink in the pits are stouter only to the extent that it remains inside without falling out. When the paper gets into contact with the back layer of the ink and stick  to the ink, due to static pressure (generated by static electricity) the Paper pulls the ink to stay on its surface.  During this process different levels of pressure is not applied on deeper and lighter areas of the engraved area, or on the Paper to pick up more ink from the deeper and lighter areas.  When  the Paper gets into contact with the plate carrying ink, it gets uniform heavy pressure from the impression cylinder to pick up the ink. See the illustration below to understand the implication of ink transfer on to the Paper during impression.

Though the print may appear  to lift  the entire quantity of ink from pits ( engraved areas) , it is true that a small  part of the ink  remain in the pit, non transferred

(6) In view of  above reason, the resultant print will not have same  amount of  relief compared to the engraved portions of the plate.  There will be marginal difference between the two- i.e engraved image and resultant print. 


(7 ) Secondly one can not feed more ink to fill up the pits and get them transferred on to Paper  as it will lead to scumming of the image i.e giving rugged edges of the prints  showing ink spots or streaks on non printing areas. Therefore only minimum quantity of  ink required to fill the pits are fed in a balancing act. 

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