Thank you very much Florian for the translation.
And what I thought impossible becomes possible.
I wondered how they did, I think I have found.
Czech workers were very good.
They made an engraved die, covering the surface with bitumen, drawing parallel lines with a needle and using a Corn-Grain screen for the place of the background, and they engraved the die by acid.
A Corn-Grain screen consists of irregularly scattered dots of irregular size and shape, and is produced by dusting a surface with a powder, usually resin or bitumen.
This is the résult for this egyptian stamp.
They made a transfer roll and used a steel printing cylinder, because this metal do not deform like copper after moletting.
And they printed stamp on Wifag, with photogravure and intaglio.
This is what explain this result.