Rotary Recess Printing.
Typography produces poorer quality stamps than recess. Typography replaced the 1st aborted attempt at recess because recess could not produce the volumes required. That all changed with introduction of the Hoe Rotary recess presses. Their introduction blew previous assumptions out of the water, specifically, for the first time, electrotyped recess plates, and, dry paper.
Although the principle is the same, the printing plate is curved to fit a rotating cylinder. As it rotates, an inked roller passes under pressure over its surface and forces ink into the recessed lines of engraving. A scraper removes the superfluous ink, and vibrating cloths are drawn repeatedly across the surface of the plate to remove all ink except that in the recessed portion. The cylinder then comes in contact with the paper, which is strongly pressed against it by a pressure roller. The curved electros are very large with up to 640 impressions on each. At nearly a sheet per second, one machine could print over half a million stamps per hour.
At first, rotary printing used steel plates. Within a few issues, they had changed to electros, and again, within a few issues they were coated with a hard nickel alloy.
Each original rotary master has pips engraved on it above (or below) each central pane of the master sheet. These were intended as guides to perforation. On each electro manufactured, these dots were enlarged by punching into the electro surface, and became the perforation guides. Variations in size and placing of these hand-made "pips" provide an infallible means of distinguishing different electros.
From 1961, plastics instead of metal were used. The first experiments consisted of making a plastic instead of a metal alto from the master plate. Later, master plates themselves were made in plastic - at first from the usual transfer roller, but later direct from the die. It was found that for relatively small issues this could lead to the cutting out of all intermediate stages between master plate and printing electro, while for larger runs new master plates could be made as required in a fraction of the previous time. Because plastic does not contract after pressing, unlike metal that contracts during hardening, stamps produced by the new process were slightly larger. There is no Australian design that used both methods for the stamp with the possible exception of the 8d zoological.