6 Colors Rotary Press Recess Printing (T.D. 6): in 1960, a new print machine has been introduced, allowing to print stamps with six different colors; the "Marianna of Cocteau" 1282 and the set of the "Birds" n° 1273/76, have inaugurated this procedure.
It allows to print sheets from 10 to 100 stamps, carnets and roulettes.
It require two print groups each usying three colors; in the first group, a metallic cylinder receive three colors from three inking rolls each carrying one color.
But, important fact, the metallic cylinder doesn't print its colors on the paper, but on a plastic cylinder of even diameter; this cylinder is a intermediary that will bring again its three colors on the paper.
These three colors constituting the shade background and they are barely delimited among them and without reliefs.
This print by the plastic cylinder is said Amount carried forward Recess Printing and it is very similar to the Offset print.
A second group of three colors, identical to the T.D. 3 print, it is printed directly with a metallic cylinder on the paper that already includes the three background shades.
With this system we can obtain overlaps of colors and creation of numerous tones impossible to obtain with the normal T.D. 3 print.
This second group of three colors brought again directly on the paper by the metallic cylinder realizes the Directed Recess Printing; it is formed by slight relief clear lines touch perceptible. The Amount carried forward Recess Printing, realized by the plastic cylinder, is performed on dry paper that comes subsequently moistened for receiving the Directed Recess Printing. Once printed the six colors, the paper goes through a drying tunnel before being wound again. There is not need of antispot paper. The paper comes subsequently indented and cut in assembled sheets to the exit from the print machine.
After the introduction of the six-color printing process (taille douce 6 or T.D. 6), Engraver's Die Proofs for some of the stamps printed on these presses, exist as Twin Engraver's Die Proofs, giving either "positive" or "negative" impressions.
Two separate dies are needed, and two separate Proofs exist, because the six-colour press prints three colors directly from the printing plate onto the paper, and three more colors by offset that requires an intermediate roller.
The first die, for the main part of the design, is thus engraved "in reverse" to print a normal positive impression.
The second die, for the background, is engraved "positively" and thus produces a negative impression that subsequently becomes positive when transferred to the paper via the intermediate roller.
It follows, therefore, that only those stamps printed on the T.D. 6 presses and using the offset facility, will require two dies and thus provide Twin Engraver's Die Proofs; while those printed without using the offset procedure will need only one die.
In particular, the large size "painting" stamps of French, Monaco and Andorra were issued in pairs (one "positive" and one "negative"), even if we can observe Twin Engraver's Die Proofs for French Antarctic, St. Pierre et Miquelon and other countries.
For definitives since 1960 some French issues, mostly the large size Art stamps, have been printed in up to six colors.
Two dies are prepared by the engraver: one for direct-recess and one for offset-recess.
Therefore two Engraver's Die Proofs are prepared, one for each die.