Introduction

In this article, we will first explain the printing principle on a TD6 press and then the way sheets of stamps are printed on such a press. We will also present the notion of phosphor band and the four types of such bands known for the stamp 0,50F Marianne de Béquet.

Printing principle on a TD6 press

A six-colour intaglio printing machine (TD6 press) is made of two printing blocks of three colours, various items for additional printings, a perforator and an output device, either in the form of sheets or in the form of booklets (cf. the article Preparation of booklets).

The first printing block is an indirect recess printing one. This first printing will have no relief (this block generally prints swaths of colour such as backgrounds). The form cylinder is engraved and the image is upright. After inking with cut touch rollers and wiping, the ink is deposited by pressure, with images back to front, on a transfer cylinder in soft plastic which, in turn, deposits ink by pressure in the face of the paper, as in offset. Printing is then dried in an infrared tunnel.

The second printing is direct line-engraving. The form cylinder is engraved, with the image upside down, to have a printing of the image upright. Inking is obtained by three hand cut touch rollers. A wiping roller removes excess ink to leave it only in the grooves of the engraving. After a second wetting of the paper, the form cylinder directly deposits ink by pressure of an impression cylinder, itself pressed by a counter-pressure cylinder. This printing is again dried and rapidly cooled on contact with hollow cylinders in which some cold water passes to create a thermal shock.

Stamps are then perforated by a comb. On a TD6 press, a comb is made of two horizontal rows of pins with the sheet of stamps width and of 11 side rows.
 

Phosphor bands (for printings with such bands) are then printed with some UV ink and immediately dried by an UV dryer. Several printing systems of these bands have been used, we shall return there farther.

Printer’s markings are printed in letterpress by a cylinder with the control number, the number of the plate used to print the sheet and the date.
 

A rotating cutting cuts each sheet to let them overlap on a conveyor belt of reception where it only remains to stack them by packages of one thousand.

It is always possible to only use a single ink reservoir to produce a monochrome printing (which is the case for the stamp 0,50F Marianne de Béquet). In this case, the touch roller will not be cut.

The drying, to avoid mixtures of colours and spots, is a major concern throughout the run on a TD6 press. A TD6 press has an infrared dryer tunnel and paper passes four times in this tunnel:

• Before printing: the paper undergoes a preheating to lose the maximum moisture. This operation, which causes an important shrinking of paper, allows to limit its dimensional variations during the drying of the indirect recess printing;

• After indirect recess printing: the paper goes back in the dryer tunnel to dry ink and to avoid any maculation and mixture of colours during the direct line-engraving printing;

• After direct line-engraving printing: this new passage allows to dry ink of the direct line-engraving printing and, thus, to perform the latest operations of sheet numbering, perforation and cutting;

• After printing phosphor bands.

Finally, stamps, once printed, are sent as parcels of 1000 sheets, probably to one post office by department. For that purpose, the printing office of Boulazac printed labels which appeared on the sent parcels:
 

Printing method of TD6 sheets

Every tour of the gravure printing cylinder prints bottom up three 100 stamps sheets, numbered from 00000 (= 100 000) to 00001, separated by a stamp height gutter, in which the guillotining of sheets will be performed.

The first sheet (sheet A on the figure on the left) has an {{electronic mark}} ( R.E. in French) on the left of stamp location 91 (it is worth noting that electronic marks are hand-engraved on the gravure printing cylinder to allow the electronic tracking of the second printing and of the perforation after optical character reading. Being hand-engraved, they have different shapes and are at different locations from each other with regard to stamps. This enables philatelists to describe and to study them). Sheet B has no mark and sheet C has two fine red lines under the stamp location 100 (for some printings, the two red lines are located in the left corner; for other editions, the two lines are not inked. This information will be given in the section about the description of printings).

On the following figures, we show the three dated plate blocks of 20 stamps printed by a single turn of a gravure printing cylinder (i.e. three sheets with consecutive control numbers). One can see the two red lines of the cylinder AG on the dated plate block numbered 10913 and the electronic mark of the same cylinder on the dated plate block numbered 10911.

Philatelists (cf. SOCOCODAMI's books for example) used to describe printings thanks to gravure printing cylinders and to characterize these cylinders by means of the two red lines appearing in the right corner of one in three sheets of stamps. We would like to recall here how these cylinders are characterized.

The two red lines are respectively called S (for Superior) and I (for Inferior). They are defined by the distances in millimetres between each of these lines and the bottom of the stamp situated just above (cf. the opposite image). For example, cylinder T is described on SOCOCODAMI's book on Béquet by:

S = 4 3/4, I = 5 3/4, short lines to the right.

The control number is located under stamp location 91, the plate number TD6-x (x = 1 to 7) under stamp location 95, 96 or 97 and the printing date under stamp location 100.

A 100 stamps sheet measures approximately 285 mm high and 230 mm wide. Side margins are white and pinked, high and low margins white and vertically perforated.

Phosphor bands

Luminescence is the property that have certain substances to restore in the form of photons part of the energy absorbed during an excitement of a certain type (electric, chemical, mechanical, light energy,...). Fluorescence and phosphorescence are two different forms of luminescence: for fluorescence, the emission of photons is visible as long as the absorbed source of energy is active. For phosphorescence, the brilliance persists during a few seconds after the extinction of the source of energy, phenomenon which is called persistence.

Phosphor bands used for French stamps correspond to the above definition, ultraviolet light being used as source of energy of excitement, as shown by a note of the general management of the French Post authorities in 1973:

These strips are overprinted using letterpress or flexography. In the following paragraphs, we’ll briefly describe these two printing methods.

Type printing

In letterpress printing, it’s the relief that does the printing. The engraver uses a chisel to remove the parts of the design that are not to be inked. The steel, copper or boxwood is engraved upside down to the dimensions of the stamp. For a stamp printed in several colors, the engraver makes several punches, each corresponding to a different color. This “original punch” is then multiplied. As a result, the cuts must be clean and sharp, as the various subsequent operations may weaken the line.

We now turn to the operating principle of a rotary letterpress.
 

 
On this machine, you will find, in order of sequence (the numbers correspond to those shown in the figure above):

1a The spool holder;

1b The gum breaker;

2 The paper feed cylinder block (known as the “call” cylinder), developed to match the size of the stamp sheet (22 times 20x26 mm). This block comprises 3 cylinders. The top one is free, the middle one is driven, the bottom one is in contact and, by pressure, “calls” the paper size. Pressure adjustment is achieved by means of threaded rods pressing on springs;

3 The first printing block (using black ink) contains the number, the date and the press number;

4 The second printing block (using colored inks) prints the postage stamps;

5 The second calling cylinder, of the same diameter as the first, has recesses corresponding to the width of the stamps. This is to avoid contact with the ink on the figures, which is not yet dry. This block ensures that the paper web is fed and tensioned horizontally between the printing and perforating blocks;

6 The perforating block, the “sheep” and its tool, the perforating “set”;

7 The sheet cutting and delivery system on this machine is reciprocating, and consists of a steel blade that moves up and down, cutting the paper like a chisel. To achieve this, “fingers” block and stop the paper during cutting. On other machines, the output is rotary, with an angled blade that cuts the paper by pressing on a metal part, without stopping the paper;

8 The sheets exit and pile up on a “belt” of two metal strips with compartments that shift every hundred sheets.
 

Flexographic printing

Flexography is a direct printing technique that uses a flexible, raised plate to deposit ink (often solvent or UV ink) on a substrate (often compared to the operation of a large-scale ink pad). This plate, initially made of rubber and since the 1970s of photopolymer, transfers ink onto a variety of materials, including corrugated cardboard, paper, plastic and even fabric.

Flexography uses a plate cylinder, an inking unit and a counter-pressure cylinder. The principle of flexographic printing is virtually the same as that of letterpress printing, in which a plate and a cliché are brought into contact.
The inking unit measures and controls the ink applied to the plate. This unit generally consists of an anilox roller dipped in an ink reservoir.

1. Anilox is dipped into the ink tank
2. A doctor blade removes excess ink
3. The anilox roller deposits the ink on the cliché, which is fixed on a cliché cylinder.
4. The ink is transferred to the substrate by light pressure from the counter-pressure cylinder.
 

 
The plate cylinder can be installed on any printing unit of a rotary press.

Plates can be produced using two techniques:
– by molding: from a flat metal form, a hollow impression is obtained, called a blank, which is used to mold the flexible material (plastic or rubber) to produce a relief plate;

– light-activated copying (exposure): to obtain a plate, a photosensitive plate is exposed through a printed or drawn countertype. Exposure takes place in a vacuum, using an ultraviolet (365 nm) exposure unit. The transparent areas of the countertype allow the ultraviolet rays to pass through, the gelatin hardens, the blacks are not affected by the rays and the gelatin remains soft - it can be removed by immersing it in a developing bath (usually sodium hydroxide diluted in water).

Phosphor band classes

According to J.J. Rabineau’s work (see reference 20), four types of phosphor bands, denoted A, B, C and D, were defined for the first issues of stamps with phosphor bands (other types of phosphor bands will appear after the disappearance of the Marianne de Béquet and will not be described here). The characterization of each type of phosphor bands can be found below (the images come from the site LES BARRES PHOSPHORESCENTES ET LEURS VARIETES):

Type A bands

• Ink is viscous, thick and matt to the naked eye, hardly discernible in daylight ;

• Bands, which seem homogeneous under UV light, are printed in letterpress (by means of a metallic printing plate covered with bronze) and naturally dried.
   

  

   

  

   

Type B bands

• Ink is fluid (diluted with alcohol), matt, hardly discernible in daylight;

• Bands have a peripheral tide line and are more or less hollow and very heterogeneous under UV light; they are printed in letterpress (by means of a metallic printing plate covered with plastic) and infrared dried.
   

  

   

  

   

Type C bands

• Ink is viscous, thick and pasty in the naked eye, brilliant in glancing light;

• Bands are rather heterogeneous under UV light, with a more or less broad peripheral tide line; they are printed in letterpress by means of a rubber or plastic printing plate and UV dried.
   

  

   

  

   

Type D bands

• Ink is viscous, thick and slightly brilliant in the naked eye and in low-angled light, highly visible in daylight;

• Bands have a soft peripheral tide line under UV light with a more or less pronounced dotted aspect; they are printed in letterpress by means of a metallic printing plate and infrared dried.
   

  

   

The stamp 0,50F Marianne de Béquet is 20 mm wide and 26 mm tall: the figurine is 17 mm wide and 22,5 mm tall, which leaves a margin of 1,5 mm on each side. Phosphor bands are 3 mm wide and 22 mm tall.