Difference Between "Intaglio" & "Photogravure" Printings

HI,

Although I've posted this topic in one of the threads, but wanted to make it as a separate thread for the benefit of my fellow Philatelists & Collectors who wish to go to the next level & take this fascinating hobby seriously.

In this thread I'll explain the difference between "Intaglio" & "Photogravure" Printing Methods further and provide more sophisticated descriptions for both of them (in two separate posts):

Intaglio Printing is printing from the recessed portions of the printing base, so that the intensity of the design printed on the paper is in direct proportion to the depth of each recess on the printing base. This characteristic alone is common to gravure & other recess-printing processes.

Copper plate engraving & printing, direct plate printing, engraving, hand engraving, line engraving, recess engraving & printing, steel engraving & faille douce are among the more common of the terms employed to denote the processes used for the production of stamps of which the lines of the design recessed in the plate stand up from the surface of the paper.

The term most frequently used is "Line Engraving," & the stamps are often referred to, simply, as "engraved."

The principle of recess engraving is:

- Into smooth metal are cut: channels & holes (recesses).

- Ink is forced or dabbed into them, but none is allowed to remain on the surface of the metal.

- Then paper is pressed into contact with the metal & forced into the recesses.

- When the paper is taken away, it sucks out the ink, which lies on the paper in ridges & humps corresponding to the channels & holes in the metal.

- If the channel or hole in the metal is deep & large, the corresponding ridge or hump on the paper will be high & large, similarly a narrow & low ridge results from a narrow & shallow channel. The deeper the channel, the more intense the color of the ridge.

- A Line Engraved design in the metal consists of a series of channels & holes varying in depth & width; a recess engraved design on the paper consists of a series of ridges & humps, varying in height, width & intensity.

Line Engraved printing may take place directly from a printing base engraved by h& (or any combination of handwork, etching or machine work), or from a printing base produced only after many processes subsequent to the original engraving.

P.s. Direct Hand Engraving: Printing by the most crude & simple form of line engraving, termed "Chalcography," was used (i.e. Mauritius 1847 Issue).

A single design of a value of a stamp was cut by hand into a copper plate by gouging out the metal with an engraving tool known as a burin or graver.

In order to produce a printing base bearing repetitions of the design, its multiplication may be carried out by Hand, Mechanically, Galvanically or Photographically.


I'll explain the "Photogravure" Printing in the next post >>>>

Photogravure: The design is reproduced multiply onto a glass plate, usually (but not necessarily) with a step & repeat camera.

This plate, termed the "Multipositive", is used to print a carbon, a sheet of gelatin sensitized with dichrornate & backed with paper.

An image is not visible, but the areas more strongly exposed are proportionately hardened.

The carbon is then applied to a metal (copper) printing cylinder, & allowed to st& long enough to develop adhesion. The cylinder is washed with water, which not only removes the paper backing, but dissolves the unhardened parts of the gelatin as well.

The cylinder is then etched with ferric chloride solution, which attacks the metal in proportion to the degree that it is not protected by hardened gelatin. Afterwards, when all of the gelatin is removed, a printing surface with the design in recess remains; it is usually given a light chromium plating before use.

In other meaning, Photogravure is a kind of recess printing, in that the ink is contained in recesses in the printing plate.

Unlike Line Engraved recess printing, where the recesses are produced mechanically, the photogravure plate has its recesses produced by etching. The steps involved in this process are:

1) Finalisation of the accepted essay.

2) Normal negative photograph of the approved design.

3) Multipositive of 100 stamp images.

4) Carbon print of the multipositive on thin gelatin tissue, for transfer to the printing plate.

5) Chemical etching of the plate, producing recesses in the form of positive images (i.e. the deeper recesses represent areas to be dark in tone).

6) The large format stamps result from processes starting with a larger multipositive plate.


* The foregoing explanation leaves out one essential step: Screening.


Screening is necessary to break up the large solid & continuous tone areas into small dots so that the printing surface will be able to hold ink in the proper places.

There are two types of screening: Grid (Mesh), & Granular (Corn Grain).

In the "Grid" screening, the carbon is exposed to a plate bearing an image of a grid of fine lines to imprint the grid on the carbon before the "multipositive" is imprinted.

The eventual result is that the metal cylinder is etched with a pattern of tiny pits, or cells, the depth of which is in proportion to the amount of light transmitted at each point.

The light areas of the stamp design have shallow cells, which thus retain very little printing ink, & the dark areas have deeper cells.

If the screen is fine the cells will be small & numerous & an appearance of continuous tone is conveyed in the printed image.

A "Mesh" (Coarse) screen can be seen easily with the naked eye, a very fine screen may be difficult to detect even with a magnifying glass. The dots that make up the image are always evenly spaced & of the same size, except insofar as they may tend to merge in the darker areas because of ink spread.

A Corn-Grain screen consists of irregularly scattered dots of irregular size & shape, & is produced by dusting a surface with a powder, usually resin or bitumen.

This may be done on a glass plate, which can then be used in the same way as a grid screen, but the earlier procedure. The grains of resin thus protected parts of the cylinder from etching.

The printing result is the same in each case, colored areas of the design have a mottled, Granular appearance, which if it is fine gives softness to the image.

The Half-Tone (Coarse) process also makes use of a screen to break up the image into a mass of dots. However, the screen is the reverse of the grid screen & consists of a pattern of square dots.

Instead of cells, the printing surface consists of dots that are high (i.e. at surface level) in the case of Half-Tone relief printing, & essentially so in the case of lithography.

The dots vary in size with the intensity of the light coming through the screen, dark areas of the stamp design having larger dots (which may even run together).

The result in the printed stamp is a simulation of continuous tone, as with "Photogravure", but the nature of the dots is different, & the effect not so delicate, for the dots all receive the same amount of inking.

Half-Tone may be used in the preparation of plates for relief printing, lithography, & offset-lithography.


Hope it helps

Cheers

Thanks James - most interesting and much more detailed than I've seen previously.

gerry68,

I'll post some pics later

Cheers

i was only joking james no worries mate.

You can never know too much about printing methods. After all, for us stamp collectors, the printing of the stamp is a crucial step.

Intaglio Printing Method:

P.S. Some of the below images were uploaded from different Websites ...


ILLUSTRATIONS

















Intaglio Printing Postage Stamps





Egypt Essay (recess)


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Other Postage Stamps with Intaglio Printing


















Printers









I'll post scans for "Photogravure" Printing in the next post >>>>>

james, many thanks for an excellent visual presentation.

Hey James,

That is indeed a very informative set of pictures and info on the difference. You learn stuff every day on this forum.

Photogravure Printing Method:


P.S. All the scans posted her are from my ex. collection ...

As we know that, the first country used "Photogravure" printing method on postage stamps was BAVARIA 1914.




Egypt was the pioneer in using the same printing method. After the British protectorate was terminated, Egypt was declared a Kingdom on February 28, 1922, two weeks later Fouad was crowned as King.

"Photogravure" process was used in King Fuad 1st Portrait Issue postage stamps in 1923.


"Photogravure with Granular (Corn Grain)" King Fuad 1st Issue (£E1)


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"Photogravure with Grid (Mesh)" King Fuad 2nd Issue (50m BLKx4)



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Half-Tone Screen



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Very Fine Screen



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Engraving Tools





Cheers

Great stuff again james.

One question: could Very Fine Screen be
considered UNscreened ?

lithograving said:





If the screen is "fine" the cells will be small & numerous & an appearance of continuous tone is conveyed in the printed image.


If dot pattern is irregular with cells of various sizes and depths it is considered "unscreen".


Cheers

Absolutely vital reading for anyone trying to discern printing types. AWESOME JOB with the presentation and information, james. - jeff

Thank you jeff ...

Actually, such a topic is very beneficial for collectors who would like to go to the next level and become real "Philatelists"

Cheers

Really nice stuff james.

Even if you don't want to go onto being Philatelists, the explanations and examples are great food for thought. Always nice to know a little bit more about how some of your favourite stamps are designed and produced.