Sheet printing on rotary presses

From a service hallmark; fifty impressions taken with lead (twice 5x5) are assembled and the block formed is dipped in a bath of copper electroplating (more or less alloyed). A galvano type (GT) is thus obtained which corresponds to a half sheet.

Then, we take wax castings which are put in turn in the copper bath to give service galvanos (GS).

These service galvanos also include rows of parallelograms. These parallelograms that span the full width of the sheet are intended to protect the GS from the pressure wear that occurs on entry and exit. The height of these parallelograms is constant for a given GT.

Note that since April 25, 1938 (65c from Tunisia), the rows of parallelograms are replaced by horizontal bars. The Peace type is therefore the last stamp in common use with parallelograms. The next Mercury type will be the first with a horizontal bar.

With the printing of dates, the above elements are structuring to identify the prints. All this is wonderfully described in the works of Baron de Vinck...

5x5 lead print

Lead print of twice 5x5 for copper plating. The galvano type (GS)

Constitution of a sheet of one hundred stamps with two GS from which two rows of parallelograms have been cut.

Printing on the Chambon press is done through an impression cylinder on which four service galavanos: GS1, GS2, GS3, GS4 are bent for the printing of two cent sheets per complete revolution of the cylinder. Note that only one of these two sheets will have the press number printed in the central margin

Jour commun sur trois presses chambon différentes le 06/08/1932

Galvano E deuxième tirage sur la presse 10

Galvano D sur la presse 2

Galvano G sur la presse 9

Travée de presses Chambon qui pouvaient imprimer plusieurs galvanos au type Paix

Cylindres d'impression en 1934. On distingue les parallélogrammes sur l'image ci-contre.